The Queen's crown jewels were hidden in a biscuit tin underground to keep them from the Nazis

It's well known that the crown jewels — a collection of crowns, robes, and other regalia kept at the Tower of London for over 600 years — are incredibly precious.

So much so that some gems from the collection were hidden underground in a biscuit tin at Windsor Castle during World War II to keep them away from the Nazis, according to a BBC documentary.

The precious stones were placed in a Bath Oliver tin in a position where the grass could regrow and conceal the hiding place, according to The Times.

The operation was so secret that even the Queen didn't know what had happened until the filming of a new BBC documentary about the Coronation, which is set to be aired on BBC1 at 8 p.m. on Sunday, January 14.

Royal commentator reportedly Alastair Bruce discovered the story among "confidential correspondence in the Royal Collection."

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Grace Kelly and Prince Rainier
Prince Rainier III of Monaco announced their engagement in January 1956. The royal proposed to the actress with a stunning Cartier eternity band. 
Grace Kelly and Prince Rainier
The 10.5-carat diamond, surrounded by two baguettes was the second ring given by Prince Rainier. The first ring was a simple eternity band embellished with diamonds and rubies.  
Crown Princess Victoria of Sweden and Prince Daniel

Daniel Westling and Crown Princess Victoria of Sweden announced their engagement on February 24, 2009 in Stockholm, Sweden. 

Crown Princess Victoria of Sweden and Prince Daniel
The simple and single solitaire was a break from the traditional gold bands many brides sport in Sweden. However, on her wedding day, Victoria was presented with an additional diamond wedding band. 
Queen Elizabeth and Prince Philip
Prince Philip proposed in 1947 with a simple 3-carat solitaire surrounded by 5 diamonds on each side. 
Queen Elizabeth and Prince Philip
The ring featured diamonds taken from the tiara of Philip's mother, Princess Andrew of Greece. It was reportedly far too large for Elizabeth, who had it resized quickly to announce her engagement. 
Prince Charles and Princess Diana

Prince Charles and Lady Diana Spencer announced their engagement in London on Feb. 24, 1981. He proposed with a 12-carat blue sapphire ring that was surrounded by 14 solitaire diamonds, made by famed jewelers Garrad. 

It cost $36,000 to make at the time. 

Prince William and Duchess Kate
In 2010, Prince William proposed to Kate Middleton with the same ring.
Prince William and Duchess Kate

The blue sapphire and diamond ring is reportedly worth $500,000 today. 

King Felipe of Spain and Queen Letizia
Crown Prince Felipe of Spain proposed to Letizia Ortiz on November 6, 2003. 
King Felipe of Spain and Queen Letizia

The non-traditional eternity band featured 16 diamond baguettes and a white gold trim. It was designed by Suarez jewelers.

After the wedding, Letizia swapped the ring for a simpler band. 

Prince Carl Philip and Princess Sofia
Swedish Prince Carl Philip announced his engagement to Sofia in 2014 after four years of dating. He proposed with an 'unusual' ring that estimated over £10,073. 
Prince Carl Philip and Princess Sofia
The center stone is surrounded by a halo and features two split diamond eternity bands. 
King Willem-Alexander and Queen Maxima

Netherland's Queen Maxima and King Willem-Alexander got engaged in 2001 after two years of dating. The ring features an unusual color and shape. 

King Willem-Alexander and Queen Maxima

The oval-shaped orange diamond is surrounded by two additional teardrop diamonds. The color is symbolic of the color of the Netherlands. 

Experts valued the stone anywhere from £15,000 and £150,000, says The Daily Mail

Prince Andrew and the Duchess of York
Prince Andrew, youngest son of Queen Elizabeth and Prince Philip, proposed to Sarah Ferguson in 1986 with a ring by the same designer as Princess Diana's ring. The two had reportedly known each other since they were young children but divorced in 1996. 
Prince Andrew and the Duchess of York

The Duke proposed with an unusual ring -- an oval Burmese ruby flanked by ten diamonds arranged in a floral shape. The ring sits on a thin yellow and white band.

Ferguson's ring reportedly set the trend for ruby engagement rings throughout Britain. 

Prince Albert of Monaco and Princess Charlene
Prince Albert of Monaco proposed to Princess Charlene in 2010 with a stunning cut valued at over £50,000.
Prince Albert of Monaco and Princess Charlene
The 3-carat pear-shaped ring was designed by jewelers Maison Repossi and is embellished on both sides with white diamonds. 
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This correspondence was an "electric set of letters" from royal librarian Sir Owen Morshead to Queen Mary, the mother of George VI. The hiding of the precious gems was ordered by George VI.

In order to hide the precious cargo, a "deep hole" was dug in the grounds "beneath a sally port, one of the secure entries to the castle, and two chambers constructed with steel doors," according to The Times.

The work had to be covered up at night. "They dug out this fresh, very virgin white chalk and they had to hide it with tarpaulins so when the aircraft flew over at night no clue was given to the German Luftwaffe that anything was going on," Bruce wrote.

RELATED: Queen Elizabeth and Prince Philip through the years:

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Queen Elizabeth and Prince Philip through the years
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Queen Elizabeth and Prince Philip through the years
This official photograph released by Buckingham Palace to mark her 90th birthday shows Britain's Queen Elizabeth with her husband, Prince Philip, and was taken at Windsor Castle, in Windsor, Britain just after Easter 2016. Annie Leibovitz/Handout via Reuters - THIS IMAGE MAY BE USED FREE OF CHARGE, INTERNATIONALLY, FOR 14 DAYS FROM RELEASE, UNTIL FRIDAY, JUNE 24, 2016. AFTER THIS DATE, FOR USE OR REPRODUCTION IN ANY FORMAT ON ANY PLATFORM, PLEASE REFER TO ROYAL COMMUNICATIONS FOR APPROVAL. NO COMMERCIAL OR BOOK SALES. NO SALES. NO ARCHIVES. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS. TPX IMAGES OF THE DAY
20th November 1947: Princess Elizabeth, and The Prince Philip, Duke of Edinburgh at Buckingham Palace after their wedding. (Photo by Hulton Archive/Getty Images)
POUNDBURY, ENGLAND - OCTOBER 27: Queen Elizabeth II and Prince Philip, Duke of Edinburgh attend the unveiling of a statue of Queen Elizabeth The Queen Mother during a visit to Poundbury on October 27, 2016 in Poundbury, Dorset. (Photo by Mark Cuthbert/UK Press via Getty Images)
(Original Caption) Queen Elizabeth II and Prince Philip fly back from a visit to Yorkshire in an Andover of the Queen's Flight, in a photo taken during the filming of the joint ITV-BBC film documentary The Royal Family.
LONDON - JUNE 1: Queen Elizabeth II and Prince Philip, the Duke of Edinburgh chat during the Gulf Parade in London on June 1, 1991. (Photo by Anwar Hussein/Getty Images)
LONDON - OCTOBER 20: Queen Elizabeth ll and Prince Philip the Duke of Edinburgh wear safety glasses during a laser surgery demonstration at the opening of University College Hospital in London on October the 20th 2005. (Photo by Anwar Hussein/Getty Images)
1947: H R H Princess Elizabeth and Philip Mountbatten, Duke of Edinburgh, on the occasion of their engagement at Buckingham Palace in London. (Photo by Fox Photos/Getty Images)
Queen Elizabeth, Prince Philip, Prince Andrew and Prince Edward waving to the crowds from the balcony at Buckingham Palace, during the Trooping of the Colour. (Photo by Fox Photos/Getty Images)
1947: Princess Elizabeth and Prince Philip, Duke of Edinburgh at Buckingham Palace shortly before their wedding. (Photo by Hulton Archive/Getty Images)
DUNSTABLE, UNITED KINGDOM - APRIL 11: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 48 HOURS AFTER CREATE DATE AND TIME) Queen Elizabeth II and Prince Philip, Duke of Edinburgh feed bananas to Donna, a 7 year old Asian Elephant, as they open the new Centre for Elephant Care at ZSL Whipsnade Zoo on April 11, 2017 in Dunstable, England. (Photo by Max Mumby/Indigo/Getty Images)
Princess Elizabeth with her husband Philip, son Charles and daughter Anne. She is the future Queen Elizabeth II of England. (Photo by � Hulton-Deutsch Collection/CORBIS/Corbis via Getty Images)
(Original Caption) Christmas at Windsor Castle is shown here with Queen Elizabeth II and Prince Philip shown putting finishing touches to Christmas tree, in a photo made recently during the filming of the joint ITV-BBC film documentary, The Royal Family.
LONDON, UNITED KINGDOM - JUNE 21: Queen Elizabeth ll and Prince Philip, Duke of Edinburgh attend the Gulf War Victory Parade in the City of London on June 21, 1991 in London, England. (Photo by Anwar Hussein/Getty Images)
ICELAND - JUNE 25: The Queen And Prince Philip In Iceland. (Photo by Tim Graham/Getty Images)
Queen Elizabeth II, accompanied by Prince Philip, sits in the House of Lords before delivering her speech at the State Opening of Parliament May 14. Prime Minister Tony Blair committed his new Labour Government to a major programme of constitutional reform aimed at making a decisive break with 18 years of Conservative rule. BRITAIN
Queen Elizabeth II and Prince Philip arrive for the start of Royal Ascot on Ladies Day June 17. The Queen, who is a keen racing fan and owner, had a winner with her horse Blueprint on the first day of the meeting. AS
Britain's Queen Elizabeth II stands on the balcony with Prine Philip, the Duke of Edinburgh at Buckingham Palace for the Trooping the Colour ceremony to honour her official birthday June 16, 2001. Trooping the colour has honoured the sovereign's official birthday since the 17th century and dates back to the earliest times of armed conflict, when each leader needed his own flag or colours to stand out clearly amid the smoke and dust of battle which led to regular trooping allowing soldiers to recognise the colours around which they should rally. BR
CANADA - MARCH 08: Royal tour of Australia and New Zealand by the King and Queen with Princess Margaret Rose early next year will be first by the reigning king. Princess Elizabeth shown here with Philip on New Zealand barque in London; will stay at home (Photo by Toronto Star Archives/Toronto Star via Getty Images)
Britain's Queen Elizabeth II (L) and Prince Philip attend the Sovereign's Parade at Sandhurst Military Academy, in south-east England, 12 April 2006. The Queens' grandson Prince Harry graduated from the elite Sandhurst military academy Wednesday. Officer Cadet H Wales as Prince Harry is known, will train to become a troop commander, in charge of 11 enlisted men and four light tanks -- a job that could soon see him on front-line duty in Iraq or Afghanistan. His grandmother Queen Elizabeth II, who turns 80 on April 21, and father Prince Charles both turned out for the passing-out ceremony where Harry and 218 other officer cadets in crisp blue uniforms, each carrying thin silver swords, received their commissions after 44 weeks of gruelling training. (Photo credit should read CARL DE SOUZA/AFP/GettyImages)
Princess Elizabeth (later Queen Elizabeth II) and Prince Philip make their way down the aisle of Westminster Abbey, London, on their wedding day, 20th November 1947. Original Publication: Picture Post - 4438 - Royal Wedding - pub. 1947 (Photo by Bert Hardy/Picture Post/Hulton Archive/Getty Images)
Queen Elizabeth and Prince Philip, Duke of Edinburgh leaving Westminster Abbey after the annual Maundy Ceremony, 7th April 1966. (Photo by Central Press/Getty Images)
Britain's Queen Elizabeth and Prince Philip watch the sack race at the annual Braemar Highland Gathering in Braemar, Scotland, Britain September 5, 2015. Queen Elizabeth will become Britain's longest-ever serving monarch on September 9. REUTERS/Russell Cheyne TPX IMAGES OF THE DAY
Queen Elizabeth II and Prince Philip at the dedication of a Knights Bachelor temple at the church of St. Bartholomew The Great, London, 10th July 1968. (Photo by George Freston/Hulton Archive/Getty Images)
390922 07: Britain''s Queen Elizabeth, Prince Philip and Prince Andrew arrive in a carriage June 21, 2001 at Ascot Racecourse in Ascot, England. (Photo by Anthony Harvey/Getty Images)
Queen Elizabeth II and her husband Prince Philip talk as they watch a calvary display by the elite Cadre Noir riding college in Paris 06 April 2004, on the second day of a three-day state visit to mark the centenary of the Entente Cordiale, the colonial-era promise of cross-channel friendship between Britain and France. AFP PHOTO/POOL/ERIC FEFERBERG (Photo credit should read ERIC FEFERBERG/AFP/Getty Images)
The Queen & The Duke Of Edinburgh Attend A Service Of Commemoration To Mark The Bicentenary Of The Abolition Of The Slave Trade Act At Westminster Abbey, London. (Photo by Mark Cuthbert/UK Press via Getty Images)
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LONDON, ENGLAND - NOVEMBER 01: Queen Elizabeth II and Prince Philip, Duke of Edinburgh attending the Official Ceremonial Welcome for the Colombian State Visit at Horse Guards Parade on November 1, 2016 in London, England. The President of the Republic of Colombia Juan Manuel Santos and his wife Maria Clemencia Rodriguez de Santos are paying their first State Visit to the UK as official guests of Queen Elizabeth. (Photo by Mark Cuthbert/UK Press via Getty Images)
WINDSOR, ENGLAND - NOVEMBER 27: Queen Elizabeth II and Prince Philip, Duke of Edinburgh greet His Highness the Amir Sheikh Sabah Al-Ahmad Al-Jaber Al-Sabah of Kuwait at a Ceremonial Welcome Windsor Castle on November 27, 2012 in Windsor, England. (Photo by Samir Hussein/WireImage)
Britain's Queen Elizabeth II (L) arrives with Prince Philip, The Duke of Edinburgh (R) at Westminster Abbey in London, for a service to mark the Passing of The World War One Generation, on November 11, 2009. Queen Elizabeth II led Britain in marking Armistice Day on Wednesday -- along with troops on the frontline in Afghanistan -- while commemorating the passing of the World War I generation of soldiers. At 11:00 am (1100 GMT), 91 years since the Great War armistice came into effect, people fell silent for two minutes to remember those who fought and gave their lives in the 1914-1918 conflict. AFP PHOTO/Adrian Dennis (Photo credit should read ADRIAN DENNIS/AFP/Getty Images)
LONDON, ENGLAND - NOVEMBER 18: Queen Elizabeth II and Prince Philip, Duke of Edinburg leave after the State Opening Of Parliament on November 18, 2009 in London, England. Queen Elizabeth II unveiled the Government's legislative programme in a speech delivered from the Throne in The House of Lords. This new session of Parliament will only last until the general election which has to be called by June 3, 2010. (Photo by Toby Melville/WPA Pool/Getty Images)
Britain's Queen Elizabeth II (L) and Prince Philip, Duke of Edinburgh (R), watch a performance during a visit to re-open the tea clipper Cutty Sark in Greenwich, east London, on April 25, 2012. The Cutty Sark, built in 1869 was one of the last and one of the fastest tea clippers to be built. The Cutty Sark was badly damaged by fire on in May 2007 but after a 50 million GBP (80.6 million USD) restoration project the vessel is restored and will reopen to the public on April 26. AFP PHOTO / POOL / KIRSTY WIGGLESWORTH (Photo credit should read KIRSTY WIGGLESWORTH/AFP/Getty Images)
LONDON, ENGLAND - OCTOBER 22: Queen Elizabeth II and Prince Philip, Duke of Edinburgh bid farewell to President of the Peoples Republic of China, Mr Xi Jinping and his wife, Madame Peng Liyuan at Buckingham Palace on October 22, 2015 in London, England. The President of the Peoples Republic of China, Mr Xi Jinping and his wife, Madame Peng Liyuan, end a State Visit to the United Kingdom as guests of The Queen. They stayed at Buckingham Palace and undertook engagements in London and Manchester. The last state visit paid by a Chinese President to the UK was Hu Jintao in 2005. (Photo by Chris Jackson/Getty Images)
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Britain's Queen Elizabeth and Prince Philip leave Horseguards Parade after the annual Trooping the Colour ceremony in central London, Britain June 11, 2016. Trooping the Colour is a ceremony to honour Queen Elizabeth's official birthday. The Queen celebrates her 90th birthday this year. REUTERS/Dylan Martinez
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THE QUEEN AND PRINCE PHILIP ARRIVE AT A PRIVATE PARTY FOR BRITAIN'S QUEEN ELIZABETH AT THE RITZ HOTEL IN LONDON.
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The Jewels were then locked inside, only accessible through a trapdoor, which still exists.

The most precious jewels — the Black Prince's Ruby and St Edward's Sapphire — were even removed from the Imperial State Crown and kept separately in the biscuit tin "in case of emergency."

A similar tin of vintage Fortis Bath Oliver Biscuits — made in England but belonging to a user in India — can even be bought on eBay for $67.50 (£50).

Speaking to the Queen for the BBC documentary, Bruce told Her Majesty — who had been only 14 at the time — the story.

"What was so lovely was that the Queen had no knowledge of it," he said. "Telling her seemed strangely odd."

He added that Her Majesty had been aware that the jewels were hidden at Windsor by 1940, when the government was trying to hide stocks of water, but had no idea where they were buried — or that they were hiding in a biscuit tin.

The tell-all documentary will see the Queen talking about her Coronation, including what it's really like to wear a heavy crown and robes.

She reportedly jokes that you "cannot look down" while wearing the 2lbs, 13oz Imperial State Crown or you neck would "break."

 

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