The Queen still uses the Imperial State crown at some events.
Mr Bruce said: "If you look very closely, the table suddenly just goes "woomf" and the crown "woomf" and the crown jeweller is left there with nothing and she says, "well you know, it's my crown". The crown is worn by the monarch when delivering a speech for the State Opening of Parliament.
The mysterious notes are addressed to Queen Mary from George VI and detail a cunning plan to bury the crown jewels under a sally port (a secret entrance to the castle) in separate chambers.
"Fortunately, my father and I have about the same sort of shaped head", the Queen said, drily. "Because if you did, your neck would break and it [the crown] would fall off", she said smiling. I mean it's only sprung on leather. The Queen said she particularly likes the Black Prince's Ruby in the crown, which was reputedly worn by King Henry V in 1415 at the Battle of Agincourt.
The queen quickly replied'You think they were at Windsor? Hmm did he remember where he put them? He might have died in the middle
In a rare conversation, she recalls her father, George VI, asking her to write down what she remembered of the day, describing the experience as "very valuable".
"So there are some disadvantages to crowns, but otherwise they're quite important things", Elizabeth added.
The Queen also recounted the day of her coronation, and how she was brought to a halt when her robes ran against the carpet pile in Westminster Abbey. "We were only children then", the queen says in "The Coronation", according to Town and Country magazine.
The precious jewels that adorn the British crown were once stashed in biscuits to hide it from the Nazis during the Second World War.
"He [Morshead] just gorged them out, recognizing there would be plenty of chances to put them back in again, wrapped them up and put them in the Bath Oliver tin so should anything happen - just as when Oliver Cromwell ordered the Crown Jewels to be smashed up - they could ferry these away and could rebuild it in due course", Bruce told The Times.