Gemstones from the crown jewels were stored in a biscuit tin and hidden underground at Windsor Castle during the Second World War.
It was already known that the gems were taken to Windsor Castle so that they could not fall into Nazi hands following an invasion, but little else was known.
Now, a BBC documentary focusing on the crown jewels and the Queen's coronation promises to reveal how the artefacts were kept in a deep hole following orders from King George VI.
The precious stones were placed in a biscuit tin and buried under a sally port - a secret exit from the castle used in times of emergency.
The Queen spent the war at Windsor Castle and knew about the story but was unaware of the details until the documentary’s presenter, royal commentator Alastair Bruce told her.
Mr Bruce told The Times:
"What was so lovely was that the Queen had no knowledge of it. Telling her seemed strangely odd."
Oliver Urquhart Irvine, the librarian, and assistant keeper of the Queen's Archives researched the story for the documentary.
The Royal commentator told the newspaper how "an electric set of letters" from Sir Owen Morshead, the Royal Librarian, to Queen Mary, the mother of George VI, shed light on the mystery.
Sir Owen's documents describe a hole being dug in chalk earth with two chambers sealed by steel, all covered to hide it from enemy bombers.
The trap door used to access the biscuit tin still exists today.
This week we spoke to Major David Rankin-Hunt, the protocol adviser for hit Netflix series: The Crown.
Looking at the crown, the Queen said: "Fortunately, my father and I have about the same sort of shaped head. But once you put it on, it stays. I mean, it just remains on."
"Yes. And you can't look down to read the speech, you have to take the speech up. Because if you did your neck would break, it would fall off.
"So there are some disadvantages to crowns, but otherwise they're quite important things."
The crown was made in 1937 for George VI's coronation and is set with 2,868 diamonds including 17 sapphires, 11 emeralds and hundreds of pearls, including four known as Queen Elizabeth I's earrings.
It also features the Black Prince's Ruby, believed to have been worn by Henry V in his helmet at the Battle of Agincourt in 1415.
The Coronation will be screened on BBC One at 8pm on Sunday.