LONDON - Sydneysiders will be waiting another 63 years to unlock a piece of history written by the late Queen Elizabeth II, with no one but her knowing what it says.

A letter was handwritten by Her Majesty herself in November 1986 when she arrived for a state visit, and is kept in a vault at the historic Queen Victoria Building, with not even the Queen’s personal staff knowing what she wrote, the website History of Sydney documents.

The only thing that can be read for the moment are instructions on the outside of the letter, addressed to the future Lord Mayor of Sydney.

“On a suitable day to be selected by you in the year 2085 A.D, would you please open this envelope and convey to the citizens of Sydney my message to them,” it reads.

It is also signed with “Elizabeth R” which is how she famously used to sign.

But everything else remains a mystery. At least until 2085.

The Queen Victoria Building, or QVB as it is popularly known, was opened in 1898 and named in honour of Queen Victoria’s Diamond Jubilee the year before. Queen Victoria is the great-great-grandmother of Queen Elizabeth II.

Queen Elizabeth II visited Australia 16 times

Queen Elizabeth II was the first reigning monarch to visit Australia and had done so 16 times in her lifetime — the first time just a year after she was crowned in 1953.

It is estimated that about one million people turned out to see her in Sydney on that first visit, 7 News reports.

The Queen and her husband, Prince Philip, returned in 1963 and visited regularly throughout the following decades, with her last visit being in 2011 when she met the then-Prime Minister Julia Gillard.

Following her death, the British monarch remains Australia’s head of state, with King Charles III now taking the reins.