Trained from childhood to be king, Charles III has endured the longest wait for the throne in British history.
But while his mother, Queen Elizabeth II, was crowned in 1953 with huge fanfare and national excitement aged just 25, her ageing, eldest son will attract less enthusiasm, royal commentators said.
"It will be very difficult for him in terms of following the queen," Robert Hazell, who founded the Constitution Unit at University College London, told AFP.
"The monarchy is likely to go through, I think, some testing times."
Born in 1948, Charles married Diana Spencer in 1981 and they had two sons, William and Harry, before their marriage fell apart, amid very public revelations of infidelities.
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Diana died in a high-speed car crash in Paris in 1997, aged 36. In 2005, Charles married his divorced long-term lover Camilla Parker Bowles.
The new king has long been known for his outspoken comments on topics from farming to modernist architecture, and often faced mockery and accusations of meddling, even if his environmental concerns have now become mainstream.
As king, he will have to change to be "scrupulously neutral", said Hazell.
In a 2018 BBC interview, Charles made it clear he understood he would have to stop his public campaigning.
"I'm not that stupid," he said.
But neutrality could prove difficult as Scottish nationalists push for another referendum on independence, while saying it will keep the monarchy, said Hazell.
It would be "very difficult... for the monarch to remain scrupulously neutral throughout the referendum campaign".
At the same time, Hazell praised Charles's "very strong sense of public service and public duty".
"I think that will carry him in very good stead when he becomes king."
Opinion polling by YouGov shows the prospect of Charles as monarch divides British public opinion almost equally.
In 2022, just under a third of respondents said he would not make a good king, while almost exactly the same proportion said he would.
"I don't expect that to change much when he becomes king," said Hazell.
By contrast, over 80 percent say the queen has done a fairly good or very good job.
Britain is a constitutional monarchy, with the king or queen as head of state. Support for a republic has stood at around 15 percent in the last two years.
Sensing a changing mood, the pressure group Republic began a billboard campaign in mid-2021 calling for the abolition of the monarchy.
Republic's chief executive Graham Smith said Charles's accession would be "a major turning point", with Barbados having ditched the monarch as head of state in November 2021, raising the prospect that others may follow suit.
"It's not going to be 1952 all over again," he added, referring to the queen's accession on the death of her father, king George VI.
"He's not protected by the almost impenetrable shield of deference that surrounds the queen."
By contrast, "Charles has had a lifetime of being criticised, being lampooned", he added.
Hazell suggested there may be pressure on Charles to abdicate in favour of his son William, born in 1982, and he could "conceivably" do so, unlike his mother.
Belgium's king Albert stood down in 2013, at 79, in favour of his son, as did Juan Carlos I of Spain, the following year.
For Smith, however, Charles "is not going to give up".
With public scrutiny of royal finances increasing, Charles reportedly wants to reduce the number of royals on official duties -- now around a dozen.
Several other European royal families have done this already.
However, numbers have fallen lately, with Prince Harry moving to California and Charles's brother Prince Andrew stepping down because of a furore over his friendship with the convicted sex offender Jeffrey Epstein.
Limiting royal roles is not primarily about saving money, but reducing the risk that "one of them will go off the rails", Hazell said.
Yet, this would reduce the numbers available to attend public events, he conceded.
Harry's wife Meghan complained in a sensational Oprah Winfrey interview that the couple's son Archie had not received the title "prince".
She linked this to slimming down, but also said that one or more royal had made racist remarks before Archie's birth.
"There's been no change that I know of to the rules, there's been no discrimination against Harry," Hazell said.
At the same time, Charles will be able to choose on titles, for example, including whether to make William the prince of Wales -- the title he held since 1958, Hazell said.
"Ultimately it's the choice of the monarch, whether to confer a title."
The Sun tabloid reported that Charles does not plan to make his youngest brother Edward the duke of Edinburgh, even though it was his late father's wish.
But in one of her last decisive acts over the succession, the queen settled the issue about what Charles's wife Camilla will be called, giving her blessing for "queen consort".