The British Imperial Crown is carried through Parliament in 2014. (Oli Scarff/WPA Pool/Getty Images)

Now we know where two of the largest diamonds in the world, along with other trinkets from the crown jewels of England, rode out World War II: buried in a cookie tin at Windsor Castle.

The long-secret, surprisingly humble hideout for Britain’s most precious royal baubles was uncovered by a documentary crew and made public Friday. Historians, royal watchers and even Queen Elizabeth herself had been in the dark about where her father, King George VI, had stashed the family jewels when a Nazi invasion was feared at any time.

“We were told nothing. We were only children then,” the queen says in “The Coronation,” according to Town and Country magazine. The film documenting her rise to power in 1953 will air Sunday on the BBC and, in the U.S., on the Smithsonian Channel.

It was only from the film’s host, Alistair Bruce, that the queen learned that her father had the most valuable of the jewels placed in an empty can of Bath Oliver cookies (biscuit tin, if you’re a Brit) and hidden at Windsor Castle, the royal retreat 22 miles from Buckingham Palace. Whether they were plain or chocolate-covered is as yet unknown to history.

The jewel-stashing operation was carried out during Hitler’s relentless bombing raids on London. Workers excavating the hiding place had to cover the dig at night to prevent German pilots from spotting the white chalk soil.  Some of the crown jewels — part of a collection of 140 ceremonial objects used to crown a new sovereign, open sessions of Parliament and other august occasions — were taken from their Tower of London vaults and packed in the larger of two new chambers.

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But the most precious, before they were tucked away, were pried from their exquisite settings and packed in the kind of tin that families throughout Britain would have had in their kitchens, probably to make them both innocuous and easy to grab and go in a quick evacuation.

All this was news to even the closest treasure watchers, according to Anna Keay, former curator at the Tower of London and author of “The Crown Jewels,” a lushly illustrated history of Britain’s official bling.

“I was commissioned by the collection to write the official history, and I wasn’t aware of this at all,” Keay said. “This is a wonderful piece of new information.”

Bruce, the historian who policed the “Downton Abbey” series for period accuracy, said the discovery came from his queries to the royal librarian in researching the documentary. He had asked for information on Princess Elizabeth’s wartime visits to Windsor and was soon summoned to the palace. In seeking answers, the librarian had uncovered long-unseen letters from one of his predecessors detailing the secret hiding place.

A few months later, with cameras in tow, Bruce was guided into a footman’s vestibule at Windsor, down through a trap door hidden under rugs in front of the fireplace and into an ancient sally port, basically a secret escape route from the castle. Deep within were the two war-era chambers that been dug from the chalk and flint, the jewels’ wartime home.

A thrilling moment to be sure, Bruce said, although nothing compared to the 90 minutes he spent talking with the queen herself about the jewels and the day she wore them to assume the throne, including her recollections of the “neck-breaking” weight of the imperial crown. Bruce had been seeking permission to make the film for 22 years, he said.

Queen Elizabeth II wearing the bejeweled Imperial Crown and carrying the Orb and Scepter with Cross, leaves Westminster Abbey after her 1952 coronation. (AP Photo/File)

“I wanted to bring the crown jewels, which are the best known but least understood symbols of the nation, back into awareness of the people,” Bruce said. “They are objects that guarantee certain freedoms that we take for granted.”

News of the find spread quickly among historians. It was known the king had probably stashed the jewels at Windsor, unlike the many National Gallery paintings that were hidden in a Welsh quarry hundreds of miles from the bombing, Keay said. And no surprise, really.

“I suspect there was probably reluctance on the part of the royal household to let go of them completely considering they included the biggest diamonds in the world,” she said.

Two of the stones in the collection will be familiar to anyone glued to the second season of the Netflix series “The Crown.” The show’s opening features a fantastical depiction of gold filigree growing like some kind of 24-karat fungus until it becomes the famous imperial crown, a massive white diamond at its center.

Claire Foy plays Queen Elizabeth II in Netflix’s “The Crown.”

That’s the Second Star of Africa, a whopping 66-facet, 314-carat diamond that was given to King Edward VII by the government of what is now South Africa. It was cut from an even larger stone, the original Cullinan. Its sister jewel, the 530-carat First Star of Africa, sits atop the queen’s scepter.

Among other bits of cookie-tin cargo were two other massive diamonds cut from Cullinan, the Stewart sapphire that adorned Queen Victoria’s crown and other majestic miscellany. One was the massive Black Prince’s ruby, a 170-carat spinel that Henry V wore at the Battle of Agincourt in 1415.

Keay approved of the homespun hiding place for what amounts to the crown jewels of the crown jewels as a proven dodge against would-be thieves. She pointed out that when the uncut Cullinan itself was transferred from South Africa, a decoy was shipped in the captain’s safe aboard a steamship in the company of armed detectives. The real stone, meanwhile, was sent through the mail.

At the very least, Bruce said, the jewels were ready to be tucked in food hamper if the royals had to flee through an occupied Britain.

“They had a protective covering and they looked like a box of cookies,” he said. “You’d be one degree more likely to make it through a checkpoint.”

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