Elizabeth died on Sep 8 at her Scottish summer home, Balmoral Castle.
Her health had been in decline, and for months the monarch who had carried out hundreds of official engagements well into her 90s had withdrawn from public life.
However, in line with her sense of duty she was photographed just two days before she died, looking frail but smiling and holding a walking stick as she appointed Liz Truss as her 15th and final prime minister.
Such was her longevity and her inextricable link with Britain that even her own family found her passing a shock.
“We all thought she was invincible,” Prince William told well-wishers.
The 40th sovereign in a line that traces its lineage back to 1066, Elizabeth came to the throne in 1952, Britain’s first post-imperial monarch.
She oversaw her nation trying to carve out a new place in the world, and she was instrumental in the emergence of the Commonwealth of Nations, now a grouping comprising 56 countries.
When she succeeded her father George VI, Winston Churchill was her first prime minister and Josef Stalin led the Soviet Union. She met major figures from politics to entertainment and sport including Nelson Mandela, Pope John Paul II, the Beatles, Marilyn Monroe, Pele and Roger Federer.
Despite being reputedly 1.6m tall, she dominated rooms with her presence and became a towering global figure, praised in death from Paris and Washington to Moscow and Beijing. National mourning was observed in Brazil, Jordan and Cuba, countries with which she had little direct link.
“Queen Elizabeth II was without any shadow of a doubt the best known figure in the world, the most photographed person in history, the most recognisable person,” historian Anthony Seldon told Reuters.
Transport chiefs said one million people were expected in central London for the funeral, while police say it will be the biggest security operation ever in the capital.
The tenor bell of the Abbey – the site of coronations, weddings and burials of English and then British kings and queens for almost 1,000 years – was due to toll 96 times.
“Here, where Queen Elizabeth was married and crowned, we gather from across the nation, from the Commonwealth, and from the nations of the world, to mourn our loss, to remember her long life of selfless service,” David Hoyle, the Dean of Westminster will say.
In addition to dignitaries, the congregation includes those awarded Britain’s highest military and civilian medals for gallantry, representatives from charities supported by the queen, and those who made “extraordinary contributions” to dealing with the COVID-19 pandemic.