The surprise abdication of Danish Queen Margrethe II has sparked speculation about Britain's King Charles III, who is being urged in some quarters to follow the Scandinavian royal's example.
Margrethe, 83, hands over the crown to her son Frederik on Sunday after 52 years on the throne, becoming the latest European monarch to step down in favour of a younger successor.
Spain's King Juan Carlos I abdicated in 2014, while Queen Beatrix of the Netherlands and King Albert II of Belgium both renounced their thrones in 2013.
Charles became king in September 2022 at the age of 73 after the death of his mother Queen Elizabeth II. He is also head of state of 14 other countries around the world, a hangover from Britain's colonial past.
He was the oldest heir apparent in British history and is now 75, with his age prompting inevitable questions about how long he will sit on the throne.
His heir, the more popular Prince William, will be 42 in June.
The Guardian newspaper called Margrethe's abdication "a sign of a sensible constitutional monarchy".
"He (Charles) is certainly entitled to a substantial reign after waiting so long. But not to death," it added.
Abdication, the newspaper wrote, indicates a nation able to keep its institutions "fit for purpose".
Royal biographer Phil Dampier believes Charles would be influenced by events in Denmark, especially if it protects the monarchy's future.
"It must make you wonder if in five or 10 years' time King Charles might think about doing the same if his health suffers or he just thinks it is a good time to pass on to William and (his wife) Kate while they are still young," he told the Daily Mail.
Royal observers say one reason Charles may want to remain on the throne longer is his eagerness to pursue his environmental agenda.
British monarchs are largely ceremonial figureheads and are not expected to intervene in political matters.
They have retained some constitutional powers including appointing a government, opening and dissolving parliament, and giving royal assent to new laws.
But they are in a position to influence world leaders.
Before his accession, Charles was accused of using his position to lobby government ministers on everything from alternative medicine to badger culls and helicopters in the Iraq War.
Royal historian Ed Owens said Charles - unlike his mother - appears to see himself as having a more "dynamic" style in which he "coaxes" change-makers and other heads of state into action.
"He's in his middle 70s, but he's still relatively fit, he's got his health - as far as we know - and I think he foresees that he's got to push his agenda in these first years of his reign," he told AFP.
Apart from the questions over his age Charles is under scrutiny about how he handles royal scandals, not least the fall-out of allegations about his younger brother Prince Andrew.
Andrew has been sidelined since defending his friendship with the convicted US sex offender Jeffrey Epstein, and settling a US civil claim for sexual assault without admitting liability.
There is also regular chatter about how Charles has dealt with his younger son Prince Harry's public criticisms of royal life after he and his wife Meghan moved to the United States.
A Savanta poll in January suggested that support in the UK for having a royal family had fallen to 48 percent in January from 52 percent in November.
Pressure group Republic, which campaigns for an elected head of state, said the scandals had taken a toll on the popularity of the king who was "ultimately responsible" for the royal family.
"Andrew has clearly done significant damage to the monarchy, but Charles is the one responsible," said chief executive Graham Smith.
The monarchy, according to Smith said, "is on borrowed time".
Yet a poll by YouGov in September suggested that 55 percent of Britons had a positive opinion of their new head of state compared to 44 percent 12 months previously.
Owens believes there is "a strong likelihood" that Charles, who has made efforts to appear more publicly accessible, will reign until he dies, like his mother who saw being queen a lifelong duty.
But he said the king would be wise to set out a definitive endpoint for his reign.
"I don't think an abdication is inevitable," Owens said.
"Although, in the longer term, it would be a sensible option to try and bring in fresh blood like many of the European royal families have done."