The Queen celebrates her 91st birthday today and is expected to spend the anniversary privately.
After her 90th birthday last year, which saw national festivities held in her honour, the 2017 milestone will seem more subdued.
But royal gun salutes will still echo across the capital later, fired by the King's Troop Royal Horse Artillery and the Honourable Artillery Company.
Princess Elizabeth Alexandra Mary was born at 2.40am on April 21 1926, the first child of the then Duke and Duchess of York, at 17 Bruton Street, the Mayfair home of her mother's parents, the Earl and Countess of Strathmore.
With the passing years have come milestones for the Queen.
She became Britain's longest-reigning monarch, passing her great-great grandmother Queen Victoria's record, in September 2015.
With the death of 88-year-old King Bhumibol Adulyadej of Thailand last autumn, the Queen is now the world's longest reigning living monarch.
Earlier this year on February 6, the date she became Queen in 1952, she achieved another milestone, becoming the first British sovereign to reach their Sapphire Jubilee, a reign lasting 65 years.
The Queen is thought to be at Windsor Castle, where she traditionally spends a month-long residence, known as Easter Court.
Earlier this month she invited British astronaut Tim Peake and others to a dinner at the castle for an event known as a "dine and sleep'' evening, where guests also spend the night.
In Hyde Park at midday, 41 volleys in honour of her birthday will be fired by the King's Troop Royal Horse Artillery.
Then an hour later the Honourable Artillery Company will fire a 62-gun salute at the Tower of London - an extra 21 for the City of London.
The Queen traditionally has two birthdays, her actual birthday and an official birthday marked every summer by the Trooping the Colour ceremony.
The curious decision to give monarchs two birthdays dates back to Edward VII, who was born on November 9 but celebrated the birthday in May and June as the weather was better during these months for outdoor events.
Subsequent monarchs helpfully had birthdays at more convenient times of the year, but the Queen's father, King George VI, reintroduced the tradition which she has continued.