-Britain's royal palaces.

Historic... -This amazing space is the grandest medieval hall in the world.

-...extravagant... -It's a magnificent fortress, but what it also is, is the world's biggest jewelry box.

-...and jam-packed with secrets.

-Sandringham is the royal party palace.

They can do what they want there, when they want, and the paparazzi can't photograph them.

-In this series, we gain privileged access inside palace walls... -All plans suggested that if they could open this up, they might be able to reveal a long-lost secret.

-...and uncover the hidden treasures within.

-We're opening boxes to find jewels with handwritten notes from members of the family inside.

-We unearth the palace's dark, secret histories.

-Underneath this beautiful palace was a secret, bubbling laboratory of horrors.

-And we reveal that the untold truth behind the palace's most dramatic modern moments... -For Harry to be made a suspect for a criminal act is really, really serious.

-I saw a gunman actually holding a gun and pointing it straight at the Queen.

-We kept it a secret, but it surprised a whole audience and quite frankly, the world.

-This is the all-new "Secrets of the Royal Palaces."

This time, we go backstage at Buck House to see Queen Elizabeth II, as she's never been seen before... -I figured that I was going to get told by the palace, "You can't shine lasers at Her Majesty, Chris.

What happens if you blind her?"

-...reveal the most controversial treasure in the palace collection... -It's connected with war, betrayal, diplomacy, colonialism, imperialism, and magic.

-...and we unlock the secrets of the monarch's occasional palace.

-This is the most important piece of furniture in the whole of the palace.

It's the sovereign's throne, and it's used by the monarch just once a year.

-But first, the palace secret of the Princess and the dancer.

It all began in 1985 with a covert phone call from Kensington Palace to the most famous hoofer in the land.

Suddenly, this voice, going, "Hello?

Is that Wayne Sleep?"

And I said, "Yes."

She says, "Oh, it's Princess Diana.

I want you to dance with me this Christmas as a surprise for my husband."

And I thought, "Oh, my."

But I knew she was tall, and I'm tiny.

I had already thought, "No [Chuckles] she could get somebody taller and better looking."

And how was I going to tell her that?

How can I say no to Princess Diana, about to be the future queen?

-And Diana's secret plan to impress Charles had a lot riding on it.

-By 1985, the relationship between Charles and Diana was not good.

We know from Diana herself that within a few months of the birth of Prince Harry in late 1984, the magic pretty much had gone out of the marriage.

-Diana later said that by this point in her marriage, she was starting to feel a bit sidelined.

She was aware that Camilla was still there in the background.

-With no time to lose, Diana arranged a clandestine meeting with Wayne at Kensington Palace.

-It's fairly easy to sneak people into Kensington Palace if you know how to, and he is only little, so you could have hidden him, I would have thought, quite easy.

-The protocol is to be searched and be questioned by the police.

But all that was taken care of.

The gates just opened, and I was on my own.

You know, met Paul Burrell at the top of the road.

He escorted me to the door, and she opened it, and we had a brief chat.

-When they secretly met for rehearsals, any doubts Wayne had disappeared.

-I walked into a rehearsal studio, and there she stood, on her own, with a headband, pink leotard, leg warmers, tights, and jazz shoes.

And she went, "Good morning, Wayne," and sort of blushed as she just ducked down.

And I was completely smitten.

[ Chuckles ] She was like a goddess, you know.

When she was at school, she won a cup for dancing, but she never danced in front of the public.

-I actually wanted to be a dancer, but I overshot the height by a long way.

I couldn't imagine some man trying to lift me up above his arms.

But I do it once a week if I can, and it's a combination of tap, jazz, and ballet.

And I really enjoy it enormously, and I think it's vital to switch off for one or two hours every week.

-To keep the dance rehearsals undercover, Diana had to sneak in and out of the palace.

-We had to keep it a secret.

Obviously, if the media or the paparazzi got hold of it, we wouldn't have been able to do it.

-She knew her husband well enough to know that if she had told him what she was up to, he'd have said, "Don't do it."

-But behind palace doors, Diana did seek a royal sign-off.

Princess Diana came to me one morning and said, "I've just had the royal seal of approval."

I said, "I thought you weren't going to tell Prince Charles and the others."

She said, "No, no, I didn't tell them, Wayne."

She said, "I've just done it for Harry and Wills, the dance.

And they applauded."

-After five months of stealth and subterfuge, at last, it was showtime.

-When I came on, I did these big jumps and spins and stuff like that, which they appreciated.

So, they were already clapping, and I thought, just you wait.

[ Laughter ] -Later, we discover how Diana's dance went down with the public and her husband.

From secret dances to secret palaces, most palaces advertise their regal status for all to see.

But there's one palace you might not think is royal at all.

-This is popularly called the Houses of Parliament, but its true name is the Palace of Westminster.

It was a royal home for centuries.

It was the principal royal palace for the English Middle Ages, right up to the reign of Henry VIII.

The thing is, it's still owned by the monarch.

And one day a year, they remind us that this place is still a royal palace.

-That day is the state opening of Parliament.

One day a year, the monarch makes their way to their occasional palace, entering at the Sovereign's Entrance, wearing the official robes of state and the one-kilo Imperial crown, before the long slog down the Royal Gallery built for Queen Victoria.

-Originally, the design for the Royal Gallery was intended to run right up to the door of the House of Lords.

That's a long space for Queen Victoria, in full regalia, surrounded by selected dignitaries, to be promenading through.

-The architects were criticized for putting the monarch too much on display, and so a little antechamber was built where she could take a moment, take a breath, and then continue down the procession route.

-And for the Queen's annual pit stop, palace designer Augustus Pugin created a masterpiece.

-The Prince's Chamber is a physical poem of the Tudor age.

You see here, amongst this dark woodwork, portraits glittering with gold and depicted fabrics of Henry VIII and his queens.

You see Elizabeth I.

Above are mural paintings showing famous Tudor naval victories.

-After enjoying a breather in style, the monarch enters the Lords.

It may appear a place for politicians, but this is the royal heart of the palace.

-This is the Lords Chamber, the most lavishly decorated room in the whole palace.

It's awash with gilding, plush red leather, and carved woodwork.

The ceiling has 18 main compartments, each adorned with various kinds of symbolism, monograms of kings and queens.

If you know where to look, you'll see the "VR" for Victoria, for whom this was made.

But the most lavish part of this most lavish room is, of course, reserved for the monarch.

This is the most important piece of furniture in the whole of the Palace of Westminster.

It's the sovereign's throne, and it's used by the monarch for the state opening of Parliament every year.

The throne itself is based on the 700-year-old throne in nearby Westminster Abbey, which has been used for the coronation of every king and queen of England since 1308.

The canopy that surrounds it is made of finely detailed oak, elaborately gilded, that includes rock crystals, embroidery, and sumptuous velvet.

All this, to be used just once a year.

-The secret to keeping the throne fit for the monarch is held by collections manager Emily Spary.

-Now, personally, I don't have many chairs at home with gilding and jewels, so is there a difference?

Any secrets in the way you clean this, as opposed to a normal chair?

-Every year before the state opening of Parliament, the throne is given a dry clean, and it's a very gentle clean, just to keep it looking shiny.

No one really touches it, except for the few inches it's moved across every year to fit in the Consort's throne.

-Because this isn't the only throne.

The monarch's other half gets one, too, with a hidden difference.

-That second throne.

It's just about an inch shorter than the sovereign's throne, and it's almost exactly the same design.

-So, there's a pecking order in the size of the thrones?

-But in 2022, the little throne got its big moment.

-Once Parliament received the news that Her Majesty the Queen wasn't going to be attending, we actually took the sovereign's throne out of the Lords Chamber, and only the Consort's throne was used for Prince Charles.

-Now, this place may be dominated by politicians, but the throne, even though it's used just once a year, is a constant reminder that the power of Parliament always refers back to the throne.

This is a royal palace.

The monarch, through royal prerogative, summons Parliament each year and could, if they wanted, kick them all out.

-Luckily, it hasn't come to that yet.

Still to come, Buckingham Palace gets a makeover for this groundbreaking photo shoot.

-The first thing I did was black it all out.

I had incense burning.

I wanted to create an ambiance of calm in the room.

-And Diana's Kensington Palace plot goes public.

-The audience responded with shock and went dead quiet.

And I thought, "Uh-oh."

♪♪ -In the summer of 1985, Wayne Sleep had snuck to the door of Kensington Palace to help Princess Diana with her secret plan.

Four months later, and Charles and Diana are leaving the palace, headed for a charity gala at the Royal Opera House.

The big night had arrived.

-Charles and Diana arrived together at the gala.

She kept everything under wraps, though she must've been feeling a bit nervous.

And then they sat together in the audience as the gala began.

-Was this a way to try and reignite some of the passion, the magic in the marriage?

Yes, I suspect it probably was.

-As the audience settled in to enjoy the show, Diana watched for her cue.

-I was going to signal to her when she should leave the box, so that she had time to get ready.

-No one in the audience knew what was about to happen.

Diana had just slipped away from Charles's side.

-She was nervous, but she was determined, after all this time, and the paparazzi not getting hold of it.

She'd won this far.

She wasn't going to let herself down now.

-But whilst Diana waited in the wings, Wayne worried.

-Anything could happen -- falling, shoes falling off, hair falling out, pins going everywhere, maybe a tack on the floor.

Anything could go wrong.

I thought when the spotlight hit her, she could actually go dizzy because it's a sea of black out there, and just a spotlight hitting your eyes.

It's like standing on the edge of the world sometimes.

-And then suddenly, she appears on stage with Wayne Sleep.

-The audience responded with shock and went dead quiet.

And I thought, "Uh-oh."

And then, the laughter just builds quietly and built and built, which was fabulous for us, because the more they did it, the more she egged them on.

Suddenly, she was realizing what performing was like, because she'd never performed in front of the public.

She was good at high kicks.

She was great with her arms.

She was good with her look, and very still, as well.

She looked great, of course, and she knew how to stand.

-She knew she was standing in front of an audience of people who knew about dance.

I mean, these were people who patronized the Royal Ballet.

There was a lot at risk here.

-And there was one risky move that had to be done.

-Well, I thought we should do a lift.

[ Laughs ] She ran to the corner.

I ran after, and she looked at me, and I picked her up and I thought, "God, what if I drop the future Queen of England?"

and ran her across the stage, you know, and put her down very lightly, and nothing went wrong at all.

-2,000 dance fans rose to their feet.

-And it grew and grew and grew till we got this eight curtain calls and an ovation.

-And she said to him afterwards, "Now I know why you do it.

Because all this curtain calls and the applause and how wonderful that makes you feel."

-And she said, "Let's do it again."

I said, "No, leave them wanting more."

-There was only one question mark over the whole performance, and that was who the performance was aimed at.

And that was Prince Charles, her husband.

What was his reaction?

I think he was mildly embarrassed by it.

I don't think he particularly thought it was a becoming thing for his wife and a member of the royal family to do.

-It has always been seen as low-class to be on the stage, and especially for women.

That was a place where your royal mistresses earned their living, not the royal wives.

-If Diana had hoped that this was going to provoke some sort of fantastic reconciliation, then it didn't happen.

-Diana may not have impressed her prince, but her secret plan delighted the public.

-I think it's brilliant that we kept it a secret, that it surprised a whole audience and, quite frankly, the world.

-Not all private palace passions are as charming as Diana's love of dance.

Three centuries earlier, St James's Palace would play host to a more grisly royal interest.

♪♪ -In the 17th century, the king built, under St James's Palace in Westminster, a secret underground lab, and that was where he engaged in the gruesome practice of skull medicine.

Charles II loved chemistry, and when he became king, what he wanted to do was buy skulls and turn them into medicine so he'd never be ill again.

The idea was that when you died a horrible death -- hanging or something else that would cause fear -- all the potency in your organs would rush into your flesh and rush into your bones.

And so, if you ate these bones or ate this flesh, you would have loads of energy and loads of potency.

The recipe is you grind down the skull of someone who suffered a violent death.

Then you mix it with ground-up deer antler and some ivory.

Mix it all up, and you've got the king's drops.

Charles thought that would cure himself and anyone else of all diseases.

So, imagine fashionable ladies dancing at St James's Palace.

Little did they know that under their feet there was a bubbling laboratory of horrors in which Charles was making medicine out of dead bodies.

-In 1684, the king's drops would be put to their ultimate test.

-Charles becomes increasingly frail.

He wakes up feeling very ill, and they immediately give him the king's drops.

Lots and lots.

40 drops, 50 drops.

It doesn't work.

He's dead four days later.

Bizarrely, the royal family keep pots of the king's drops.

It's a bit like when Grandma dies and you keep her marmalade as a memory of her.

So, when Charles II's niece, Mary II, she's on her deathbed, they give her the king's drops.

Doesn't work.

She dies, too.

They are completely and utterly useless.

-Less than a mile away from St James's Palace lies Buckingham Palace, the hub of royal business, which, when you're the monarch, includes regularly getting your portrait done.

Queen Elizabeth II sat for more than 130 portraits during her long reign.

-She used them as the monarchs have always used them, which is to commemorate her power, celebrate her longevity, and tell history, "I've been around forever.

I'm going to be around forever."

-The usual palace portrait exudes regal tradition.

But in 2003, much to the surprise of chosen artist Chris Levine... -I was the wild card in a short list of kind of household names, then me.

But when I first got the call, I thought it was a friend of mine pulling my leg.

I mean, I had been asked to shoot Indian gurus, and I had shot rock stars, but the Queen somehow seemed farfetched.

-I think it was a surprise, actually, that the Queen commissioned someone like Chris Levine, who shot Kate Moss and Grace Jones -- you know, all these iconic pop stars.

-And Chris planned to create a portrait of the Queen like no other.

-Originally, the idea was to shoot a hologram, a conventional hologram, but that would have meant taking Her Majesty into a laboratory, exposing her under laser light.

And I figured that I was going to get told by the palace, "You can't shine lasers at Her Majesty, Chris.

What happens if you blind her?"

-So, Chris selected a method less likely to disable Her Majesty.

-To make the portrait, we essentially use a camera that moves along a track and takes typically up to about 50 frames.

And each one of those frames is a different perspective view of the subject.

And then we put them, with a computer program, all together, so you read it as 3-D. -With plans in place, Chris was given a surprise extra task.

-About a week before the shoot, I got a call from the palace to say, what would I like Ma'am to wear?

Up until that time, I'd been imagining that, you know, she's the queen, she'll be wearing what she wants to wear, and I'll create the portrait on the day.

And so, I got to literally, you know, hold up one or two dresses and then chose one because it was a really simple A-line dress.

And then we went next door to the Royal Collection to look at the crown jewels.

That was mind-blowing.

These amazing creations.

But I went for what I felt was the most simple, understated.

It's the diadem, and it turns out it's a very historic -- it's a very important crown.

-Chris was given the Yellow Drawing Room in Buckingham Palace, traditionally used for portraits because of its abundant natural light.

But he promptly turned tradition on its head.

-The first thing I did was black it all out.

I had incense burning.

I wanted to create an ambiance of calm in the room.

-The Queen entered what she probably thought was some sort of opium den, but she was down with it because she didn't leave, so maybe she enjoyed the scent of patchouli.

-When the queen entered the room and I could see she was having to process what was going on in the Yellow Drawing Room -- unlike anything that's happened in there before, for sure.

I talked to her about my meditation and that I was going off on a retreat very shortly, and she said meditation -- her meditation's her gardening at Balmoral, which is really lovely.

-In the blissed-out surroundings, the Queen relaxed enough to crack a joke or two.

-One of the setups I had was a laser scanner that projected patterns onto Her Majesty's face and my sister Nina said, "Ma'am, it's just like having your passport photo taken."

Her Majesty said, "One doesn't need a passport."

-Chris took hundreds of images of the Queen.

To select the single official portrait, he headed to Windsor and made his way to Her Majesty's inner sanctum.

-I could hear the corgis in the distance, so I knew I was getting close.

And went into her study, where she does the Queen's Speech, and I was able to show her the work, and we chose the image together, which I went on to develop as the final piece.

-Chris's portrait of the Queen was released to worldwide acclaim, but in a dramatic turn of events, the story didn't end there.

Coming up, the Queen is not amused when a secret palace image goes public.

-I thought, "I'm going to the tower.

I'm in trouble."

-And we reveal the extravagance of the Queen Mother's crown.

-This has got to be the ultimate bling crown.

The whole surface of the crown just glitters.

♪♪ -In 2003, Buckingham Palace's Yellow Drawing Room was transformed like never before for the creation of a royal hologram.

But unbeknownst to either Queen or photographer, the photo shoot held a stunning secret.

-Some years later, I was going through my hard drive, and I saw the image with the Queen with her eyes closed.

And I remember that moment because there was a lot of light onto Her Majesty, and I asked if she'd like to rest in between shots, and she closed her eyes.

-Chris Levine's photograph of the Queen with her eyes closed is so chic, it could almost be in a fashion magazine.

It's a private moment.

She looks like an old-school Hollywood actress.

An icon.

-She looked very, very human.

The mask was off.

She was at rest.

She was relaxed.

It's almost like we've caught her in a very, very private moment.

But it's also very, very beautiful.

-Chris named his extraordinary image "Lightness of Being," and it was snapped up by the press.

But the palace was in the dark.

-The Daily Telegraph asked if they could put "Lightness of Being" on the cover of the magazine on Saturday, and I assumed that The Telegraph and the Palace would have spoken, and everything's cool.

And I find out on the Friday night that the Queen, whose favorite read on the Saturday is the Telegraph, didn't know this was coming out.

The Palace office didn't know it was coming out.

-The palace was not amused, and Chris was summoned for a secret meeting.

-And I really thought that was it.

I thought, "I'm going to the tower.

That's it.

It was all going so well, but I'm in trouble."

And we were given a bit of a shake-down.

It was a bit fraught.

-Days later, Chris received a follow-up call from the Queen's personal assistant.

-Angela Kelly told me that the Queen knew that I created the work with affection.

There's no disrespect to this, so it was -- the intentions were pure, were good, and I was let off.

-Stories of royal approval and royal censure have been played out in these remarkable buildings for centuries -- some petty, some touching the lives of us all.

-The royal palaces are the witnesses of the passage of time.

They have seen everything, all the major changes.

They are the backdrop to our nation's history.

-None more so than the Palace of Westminster.

The building we see today was built in the Victorian age, but hidden within its walls are the remnants of a medieval royal secret.

-This amazing space is the grandest medieval hall in the world.

It was set out at the end of the 11th century by William II, the son of William the Conqueror, and what he created was a hall 240 feet long, 67 feet wide -- by far the biggest hall in England, almost certainly the largest in Europe.

It was perfect for state ceremonial occasion, feasts, you name it.

There was nothing that could match it.

-300 years after it was first built.

King Richard II gave the hall its most impressive feature.

-What makes this such an amazing building is not just the scale, it's the phenomenal, self-supporting roof.

At a span of over 20 meters, it's a design miracle of the Middle Ages.

It's called a hammer beam, and the purpose of it is to have projecting horizontal beams from the side walls to minimize the span of the central arch, and in that way, span broader spaces.

And what not many people realize, hidden away in the darkness, is that the angels that emerge from this heavenly assembly, their feet still in the clouds, are each pushing forward a shield of King Richard II himself.

It's as if the Parliament of Heaven was stamping its approval on the reign of Richard II.

-The Palace of Westminster is so rich in history and secrets that they are still being uncovered.

♪♪ -I mean, the cloister of St Stephen's, a fabulous survival from the medieval palace.

And here, in 2018, as part of the endless restoration of the palace, an extraordinary discovery was made.

It's this -- a tiny keyhole.

Now, it doesn't look much, but old plans suggested that if they could open this up, they might be able to reveal a long-lost secret.

♪♪ It turns out they discovered an ancient passageway that linked the old Commons chamber through to the Great Hall.

Behind this blocked-up wall is the Great Hall.

Here you can see one, two, three, four iron pintles that show there were two massive doors that once hung here, side by side.

You wouldn't know about that from the other side.

But here, above our heads, you can see ancient timbers.

Oak can be dated.

And the tree that these oak beams were made from was felled in 1659, just two years before the greatest pageant of royalty this palace had ever seen.

-The route through this previously hidden tunnel into Westminster Hall was built especially for the coronation of Charles II in 1661, one of the most important royal events of all time.

-The coronation of Charles II was like no other coronation in English history.

11 years earlier, his father had been executed, and the monarchy was over.

There wasn't any reason to think that there would ever be a coronation in England again.

And so, when Charles II is crowned and has this huge coronation procession in London, not only is there a sense of great joy and great relief, but a sense of a new beginning for the English monarchy, and the coronation, the grandeur of it, really reflects that.

-This humble passageway takes us back to a triumphant royal moment.

But how was it lost?

-And here is where graffiti helps us, because it tells us that this room was enclosed by Tom Porter, who was exceedingly fond of old ale.

And the date it gives us is down here -- 1851.

For over a century and a half, this room has been forgotten.

♪♪ -Palaces have long been synonymous with banquets, and none were as famed as Henry VII's at Hampton Court.

But much of what Henry actually ate and what it tasted like has long been a mystery.

Today, Kate Williams is meeting a pioneering food historian who's been resurrecting lost palace recipes.

-Hi, Marc.

-Hello there.

-Good to see you.

You're going to be explaining to me the secrets of Henry VII's table.

Something exciting is under here, I think.

-Oh, yes.

Let's have a look.

-What is that?

What is that?

-Have you heard of lampreys?

-These are lampreys?

-These are lampreys.

-Really?

The medieval and Tudor obsession?

-Yes, they loved them.

-They're disgusting!

-They're always on the royal table.

-Look at them.

What's that?

Is that their little mouth there?

-Yes, they have a circular mouth of... -Ew!

A circular mouth?

-...many, many, many teeth, so they can latch on to a fish and suck its blood.

They're parasitic.

-Feed on the blood?

-Mm-hmm.

-These are vampire fish?

-Yeah, that's one way of putting it.

-Why were they so popular?

-I can only presume they're actually quite nice, because if something's really weird and expensive, you might put it up once or twice.

But they keep appearing.

There are lamprey dishes right through all the royal courts.

In fact, our current queen had a lamprey pie at her coronation, so they must be one of the top royal dishes.

-And Henry VIII... -Supposedly enjoyed them on his own.

-So, it's like when I'm at home, I'm having a toasted cheese sandwich on my own in front of the TV.

Henry would have had a nice -- -Time for a lamprey.

-...hob of a lamprey.

-Yes.

-But have I got to eat them like this?

-Oh, no.

We've got to prepare them.

There's lots of recipes, and they come in a lovely sauce.

Let's try lamprey.

-These lampreys are from Canada.

They died out in the UK during the Industrial Revolution, and most recipes disappeared with them.

But Marc has uncovered a lost Tudor recipe for lamprey stew as served at Hampton Court Palace.

-So, we just have to dig down and find a nice piece of fish.

That goes onto your trencher.

-What's in the sauce?

-The sauce is very exotic.

It's called a cameline sauce.

It's got cloves, ginger, sugar, red wine.

All of these things don't grow in England.

Only the lamprey and the saffron in it come from England, so it's exotic.

-So, I cut a bit off and then eat it with my fingers?

-Yes.

The sauce is really good.

I can really taste the red wine.

I quite like the fish.

It's actually -- it's actually okay.

It's quite a mild fish.

It's quite a good texture.

-Meaty, I would say.

-I like that more than I thought.

I like that more than I thought.

I think I've done a 360.

I think they were the most disgusting thing I've ever heard of, and now here I am, just so close to the idea of Henry VII having his quiet little suppers on his own with his tasty dish of lampreys.

-Henry had the use of at least 60 royal palaces, including the Tower of London.

He used it primarily to store weapons and unwanted wives.

Today, its main royal function is as a home for the Queen's jewelry.

-As jewelry boxes go, the Tower of London is the big one.

-It has the most incredible array of jewels inside -- row after row of these historic pieces that encapsulate so much of Britain's royal history.

-And perhaps no item contains more stories and secrets than the Queen Mother's crown.

-This has got to be the ultimate bling crown.

For a start, it's the only one belonging to a king or queen that's made entirely of platinum.

It has these four arms that curve over the top and they're attached to fleur-de-lis.

Then there's a purple velvet cap surrounded by ermine.

-But the thing is, with this crown, is that it is absolutely plastered in diamonds.

There are around 2,800 diamonds on the Queen Mother's crown.

The whole surface of the crown just glitters.

-The Crown was created in 1937 for the Queen Mother to wear at the coronation of her husband, George VI.

George wanted his queen to stand out, but finding 2,800 diamonds is no easy task.

It was time to ransack the peerless royal jewelry collection, as this extraordinary archive film shows.

-To make this crown, Garrard & Co. were given access and allowed to choose diamonds from various pieces that they could rework into the Queen Mother's crown.

-He ended up taking some of the diamonds.

from Queen Victoria's regal circlet.

And when you look at that circlet now, you can see that it is somewhat less regal.

-Of all the jewels purloined for the Queen Mother's crown, one is more prominent than all the rest, the Koh-i-Noor diamond.

-This is one of the most important stones in the whole royal collection.

Firstly, it's huge.

-It weighs in at 106 carats.

It is one of the most precious and beautiful diamonds in the royal collection.

-It's also one of the most controversial.

-It's connected with war, betrayal, diplomacy, colonialism, imperialism, and magic.

-And on top of that, it is allegedly cursed.

Well, that is, if you're a man.

-Coming up, the dark history of the cursed royal gem... -In Hindu legend, any man who owns it will own the world, but will also experience all of its misfortunes.

-...and the gory Holyrood invention that killed on an industrial scale.

-Now, the Maiden is actually flatpack.

It's like an Ikea guillotine.

This makes death just too easy.

It makes it just too simple.

♪♪ -Britain's royal palaces today are serene and stately, but they haven't always been so.

In the 16th century, they were often places of vicious bloodshed.

♪♪ -When Mary, Queen of Scots, came back from France to take her throne in Scotland in 1561, she expected her palace, Holyrood Palace, to be a place of grace and beauty and dignity.

That was not the case.

It was in fact a place of murder and bloody struggle.

-Holyrood Palace was the site of a grisly killing when Mary's secretary, David Rizzio, was brutally stabbed.

Months later, Mary's lover was blown up.

A key player in both killings was James Douglas, and he appeared to profit from them.

He would become Scotland's de-facto ruler in 1572, and upped the bloodshed still further with something called the Maiden.

-The Maiden was an execution machine, a one-stop execution shop.

It chops off the head, and that's that.

And the Maiden is actually flatpack.

It's like an Ikea guillotine.

This makes death just too easy.

It makes it just too simple.

And it became a modern public spectacle and claimed 150 victims.

James Douglas certainly would end up wishing the Maiden didn't exist.

He had power.

He had glory.

He had money.

But he also had enemies, and people turned against him.

He was put on trial for murder.

He was sentenced to death.

And do you know how he was killed?

He was killed by the Maiden.

So, the Maiden was what finally caused the death of James Douglas.

His corpse remains on the scaffold for the day, and then his head is put on a spike by the Tolbooth of Edinburgh.

So, James Douglas, fourth Earl Morton, who oversaw so much bloodshed, in the end, he gets his comeuppance.

-The Tower of London, the finest jewelry box in the world, gives pride of place to the cursed Koh-i-Noor diamond on the Queen Mother's crown, and it's one of the most controversial jewels in the royal collection.

-"Koh-i-Noor" literally means "the mountain of light," and it was originally mined in India.

It's always been said to carry a curse.

-In Hindu legend, any man who owns it will own the world but will also experience all of its misfortunes.

-For centuries, the diamond passed between rulers, often surrounded by bloody turmoil.

-The first record that we have of the Koh-i-Noor is from 1628.

We know then that it was set right in a very prominent position in the utterly splendid peacock throne of Shah Jahan.

-Shah Jahan's son later had him imprisoned during a coup, and so, the diamond changed hands.

In 1739, the Iranian ruler Nader Shah invades the Mughals, killing tens of thousands, and he steals the diamond.

Once again, the curse strikes.

He is assassinated in his sleep by 15 of his officers and followers.

-In 1849, the British managed to get their hands on the stone, and they did this by imprisoning the mother of the last maharaja.

He was 10 years old.

They ultimately forced him to sign off all claims to sovereignty and to the Koh-i-Noor.

-Which is how Queen Victoria got her hands on it.

She put it on display at the Great Exhibition in 1851.

-But the general consensus was that it wasn't that impressive.

-Instead of calling it the mountain of light, one press commentator called it "the mountain of darkness."

-So, Prince Albert had the diamond recut to give it more facets, more of a sparkle, but in the process, over half the diamond was lost.

Queen Victoria then wore this new, stunning, freshly cut diamond as a brooch.

Whether the British monarchy heeded the ancient curse of the diamond or not, nobody knows.

But it has only been worn by women.

And remember, the curse said no man shall wear it.

-The controversy surrounding the diamond has followed it to this day.

-Since Indian independence in 1947, the Indian government have made several demands for the Koh-i-Noor to be returned to them, most lately in 2016.

-The diamond embedded in the Queen Mother's crown was last seen on official business at the Queen Mother's funeral in 2002.

-It was very symbolically and somberly placed on the coffin of the Queen Mother.

-Since then, it has been on show in the Tower of London, seen by thousands of tourists, but its role within the royal family will continue.

-It will be used once again when Charles has his coronation and becomes king, and his wife Camilla will be declared Queen Consort.

Then, this beautiful platinum-and-diamond crown will once again sit on the head of a queen.

-Next time on "Secrets of the Royal Palaces," there's panic on the streets of London -- [ Gunshots ] ...as a loyal soldier tackles an armed gunman outside Buckingham Palace.

-This is assassination.

He's trying to kill my queen.

-We go behind the scenes at the Kensington Palace flash sale that caused a sensation.

-This is an unprecedented sale of a lifetime.

Royal possessions being auctioned off.

-And we reveal Queen Elizabeth II's secret passion for cars.

-She was probably one of the only royals in the world who can completely strip down a car engine.

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