The Queen is marking the anniversary of her accession privately as she reaches 67 years on the throne.
Gun salutes will be fired by the King's Troop Royal Horse Artillery in Green Park and the Honourable Artillery Company at the Tower of London to commemorate the occasion.
The bells of Westminster Abbey, the gothic church where the Queen was married and crowned, will also ring out to mark Accession Day.
Princess Elizabeth became Queen on February 6 1952, on the death of her beloved father George VI.
She was just 25 and thousands of miles from home on a Commonwealth tour with the Duke of Edinburgh in Kenya when the King died in his sleep from lung cancer at Sandringham House.
Now the nation's longest reigning monarch, Elizabeth II has ruled for 24,472 days, has passed her silver, golden, diamond and sapphire jubilees, and is now just three years away from her platinum 70 years on the throne.
As she does most years, the Queen is reflecting on the anniversary of her father's death in private at Sandringham, where she has been staying for her annual winter break.
The holiday has been more eventful than previous years after the Duke of Edinburgh was involved in a serious car crash involving a mother and a baby.
The Queen usually returns to London soon after her anniversary.
Here's a look at the Queen in numbers:
1 – Ranking in the list of world's longest-serving current monarchs. She moved to first place after the death of the King of Thailand in 2016.
13 – Prime ministers in office since the start of her reign, from Sir Winston Churchill (1951-55) to Theresa May.
13 – US presidents since the start of her reign.
16 – Countries of which the Queen is monarch – the UK and 15 Commonwealth realms.
21 – Age when she married the Duke of Edinburgh.
25 – Age when she became Queen.
67 – Years on the throne.
71 – Years of marriage to the Duke of Edinburgh.
72% – Proportion of her life that Elizabeth II has spent as Queen by her 67th anniversary on the throne
599 – Charities, organisations and military regiments of which the Queen is patron or has associations with.
More than 660 – Investitures personally held by the Queen since the start of her reign.
24,472 – Days on the throne on February 6 2019.
50,000 – People the Queen hosts in an average year at banquets, lunches, dinners, receptions and garden parties at Buckingham Palace. The figure for Holyroodhouse in Edinburgh is more than 8,000.
1.45 million – Approximate number of people who have attended a garden party at Buckingham Palace or the Palace of Holyroodhouse since 1952.
More than 3.75 million – Items of correspondence the Queen has received during her reign.
£370 million – The Queen's wealth, according to the Sunday Times' Rich List.