Elizabeth, Britain's longest-reigning and longest-lived monarch, was born on April 21, 1926, going on to spend 70 years on the throne before her death in September 2022 at the age of 96.
Such is her enduring impact that a recent YouGov survey found 81 per cent of those polled had a positive opinion of her - more than any living member of the royal family.
"I don't think I've ever seen anybody have a sense of duty like she had," Charles' wife, Queen Camilla, told a BBC documentary broadcast on Sunday.
"It must have been so difficult, being surrounded by much older men," Camilla said of Elizabeth's accession to the throne in 1952, aged 25.
"There weren't women prime ministers or women presidents. She was the only one, so I think she carved her own role."
Charles and Camilla will visit a new exhibition, Queen Elizabeth II: Her Life in Style, currently at Buckingham Palace, to mark the anniversary of her birth.
More than 300 items, ranging from the late queen's wedding dress to the outfit she wore for her cameo appearance at the opening of the London 2012 Olympics, are on display in the largest-ever exhibition of her wardrobe.
Famed for wearing bright colours and matching hats, she once quipped: "I have to be seen to be believed."
On Tuesday, the king and other royals will visit the British Museum to view the final designs for a national memorial to his mother, while Charles' sister, Princess Anne, will officially open the Queen Elizabeth II Garden in London's Regent's Park.
In the evening, Charles and Camilla will host a reception featuring representatives from charities his mother supported as well as a number of people celebrating their 100th birthday.
The royals' commemorations come after the government announced on Sunday a new independent charity, the Queen Elizabeth Trust, was being launched to focus on restoring shared spaces in communities.
The trust is being backed by STG40 million ($A75 million), with the King as its patron.
