The Queen celebrates her 95th birthday this week, just days after farewelling her husband Prince Philip, and the impressive milestone will mark the start of Prince Charles' transition to king of England.
Charles, who has been king in waiting for the seven decades of his life, will now become the"king in training".
He, and in turn Prince William, will step up to represent the Queen in her final years as the world's longest reigning monarch.
Royal experts say the Queen will never abdicate, which would make Charles "Prince Regent", or stand-in sovereign.
Instead the Queen will "carry on" in her life's role leaving Charles to inherit the throne on her death.
This is just as she did, albeit at an age probably 50 years younger than Charles will be, when her father King George VI died in 1952 and she was crowned the following year.
She pledged back then: "I declare that my whole life, whether it be long or short, shall be devoted to your service."
Robert Jobson, author of Prince Philip's Century, said the Duke of Cornwall will move into more of a front seat role making appearances in the Queen's stead for events like state visits.
At the age of 72, Charles will become Britain's "quasi-king", Jobson told ABC podcast, The Heir Pod.
Jobson had used the term during coverage of the Duke of Edinburgh's weekend funeral, acknowledging the royal family would hate it but that it encapsulated Charles' new role.
"The Prince of Wales will step up, in a way he's already been doing that for the past five years, but now he truly is the patriarch of the family because the Duke of Edinburgh is dead," Jobson said.
"The fact is the Queen doesn't do state visits anymore, so when Prince Charles goes to America say, he'll be representing the Queen.
"That's pretty much a state visit even though it's technically not."
Commentators remarked that the Queen struck a solitary figure during the Duke's funeral, necessitated by coronavirus restrictions, but poignant nonetheless.
For the first time, the stoic and energetic monarch looked "frail" when she made a slight misstep entering St George's Chapel, and paused to look back at her husband's coffin.
"She (the Queen) looked a little unsteady on her feet and the Dean, David Conner, supported her in I think," Jobson said.
"I thought she looked frail at that stage (but there is) no doubt that the Queen will carry on.
"She'll never, ever abdicate the throne."
But the fact is with Prince Charles more in the forefront, a de facto regency will be in place.
It is a new era for the royals, with the second heir in line, Prince William, who should eventually take his father's role as the next Prince of Wales, taking a more prominent role.
London newspapers have reported the Queen has moved out of Buckingham Palace where she lived with Prince Philip.
At her new permanent home at Windsor Castle, she will continue royal obligations, such as receiving the red boxes of government business and her weekly audience with the British Prime Minister.
However, it is expected Charles will take over duties such as meeting the diplomatic representatives of Commonwealth countries, which take place at Buckingham Palace, The Sun reported.
With his wife Camilla, the Duchess of Cornwall, Charles' diary will assume more royal engagements, allowing British subjects to adjust to the idea of his kingship while still having their Queen.
Public opinion has wavered over the popularity of Charles as the next king, with some opining the succession should just leapfrog him in favour of William.
The organic farming, "talks-to-plants" prince is not every Brit's cup of tea, but royal commentators say he will be crowned king.
Camilla will be entitled to be called Queen, but may opt instead for the title of Princess Consort, knowing no one can replace the Queen and it would be foolish to do so in name.
And when his father accedes the throne, Prince William will inherit Charles' Duchy of Cornwall, the precursor to being crowned Britain's monarch.
William and Kate will move to the 52,789ha estate with their children who are third, fourth and fifth in line to the throne.
The Queen is expected to live, like the Queen Mother, to over 100, and although she will gradually withdraw from state duties she will remain on the throne.
Immediately upon her death, Charles will become King of England, the British national anthem will change to God Save Our King and the mourning will be loud and long.
But with perhaps a five-year period of adjustment and Charles' backing by his mother as right and proper for the role, the monarchy is set to enter its next, post-Elizabethan age.