Queen is first British monarch to reach Sapphire Jubilee after 65-year-reign
February 6, the anniversary of the day she became Queen, marked 65 years of Elizabeth II's reign.
But there are no grand festivities planned to mark the head-of-state's new milestone.
The Queen is not due to be out and about on official engagements on the landmark day.
As is usual on Accession Day, she will be spending it privately at her Sandringham Estate in Norfolk.
She was in good spirits on Sunday as she greeted well-wishers after attending a church service at St Peter and St Paul in West Newton, Norfolk.
Three-year-old Jessica Atfield, who dressed specially for the occasion in a union flag skirt, was delighted when she handed a bunch of flowers to the Queen.
The Queen, who missed church over Christmas due to a heavy cold, will undoubtedly be matter of fact about the historic occasion.
In 2015, when she thanked the nation for the kind messages after overtaking Queen Victoria to become the longest-reigning monarch in British history, she admitted bluntly that the royal record was ''not one to which I have ever aspired''.
She added: ''Inevitably, a long life can pass by many milestones. My own is no exception.''
The Queen celebrated her 90th birthday last year and had a busy schedule commemorating the occasion, with a walkabout, beacon lighting and a black tie dinner for family and friends in Windsor on her actual birthday.
A weekend of national celebrations, including a party on The Mall, was held for her official birthday in June.
It is likely that any large-scale jubilee celebrations will be reserved for the Platinum Jubilee in 2022 - although any events will take into account the fact that Queen is due to turn 96 that year.
The Duke of Cambridge is about to become a full-time royal this summer and will increase his official duties on behalf of the Queen.
William and the Duchess of Cambridge are carrying out an engagement on Monday, but not to do with the Queen's record-breaking reign.
They will be attending Place2Be's Big Assembly at a primary school in north London to mark Children's Mental Health Week.
The anniversary of Elizabeth II's accession to the throne in 1952 is a poignant time for the Queen, marking the day her father George VI died.
She often spends Accession Day privately at Sandringham, staying there through the Christmas period. She usually makes her return to Buckingham Palace a few days later.
Royal gun salutes will be staged in London on February 6, as is the tradition.
A 41-gun salute will be fired by the King's Troop Royal Horse Artillery in Green Park at noon.
The Band of the Royal Artillery will play a selection of celebratory music close to the firing position, and 89 horses will pull six First World War-era 13-pounder field guns into position in the park.
A 62-gun salute by the Honourable Artillery Company will be fired at the Tower of London at 1pm.