A monarch willingly giving up their throne is a historic occasion in any country.
But that's even more true in the United Kingdom, where it's only happened once in hundreds of years of monarchy.
When King Charles III was diagnosed with cancer, royal experts were suddenly being asked to consider the prospect of another abdication.
Few believe the man who waited seven decades to become King will abdicate, but a number of questions remain if he does.
What would happen next, how would it differ from a more traditional transfer of power, and what would it mean for Australia and the other countries that keep the British monarch as the head of state?
What is abdication?
Put simply, it's just giving up the throne and passing it on to the next king or queen.
The prime minister needs to be notified, followed by the signing of what's known as an instrument of abdication.
The next step is for the Accession Council to meet and proclaim the new king.
How is it different from succession by demise?
Procedurally it's not that different, really.
There are a couple of small differences mostly relating to Charles and Queen Camilla's titles.
But for all intents and purposes, most of the processes are the same as those prepared under Charles' standard succession plan, reportedly called Operation Menai Bridge.
Who would become King?
As the heir, William would become King the moment Charles abdicated or, if his health deteriorated further, passed away.
What would happen to Kate, Camilla and Charles' titles?
This question is a little bit more complicated.
If Charles were to pass away, royal historian Kelly Swaby said Camilla would become the Dowager Queen while Kate would come to be referred to as Queen Catherine.
But if he were to abdicate, the rules are not as certain.
"I suppose King Charles would just be known as King Charles, not King Charles III," Swaby said, explaining that the numbering denotes the current monarch.
"So in that sense, Camilla would keep the title but her title depends on what Charles' title is.
"And again, that's a very interesting discussion that I don't think many of us have contemplated."
Would Charles really abdicate?
It's impossible to say definitively because we don't know Charles' thoughts or the full details about his health.
But the overwhelming answer from those in the know is a fairly resounding no.
"I don't think he will go anywhere anytime soon," Joe Little, managing editor of Majesty Magazine, said.
"I still think that abdication is not a word that is bandied about at Buckingham Palace.
"I mean, who knows what the coming years will bring, but with the best will in the world, Charles III will reign as his mother did, and until the moment of his death."
Swaby agreed, saying she couldn't see it happening "under any circumstance".
"I think Charles, after waiting so long to be King, and after a man who has, you can tell, a deep sense of duty and he feels like he has an obligation to carry out the duties, I just can't see him abdicating," she said.
"I would be incredibly shocked if he did but at the same time, I think a lot of us, given the cancer diagnosis, would also be understanding if that decision ever came.
"But I honestly, on the balance of probability, just don't see it happening. It's not impossible, but it's highly unlikely for me."
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Why is abdication such a dirty word in the UK?
There is more than 1000 years of history behind the country's aversion to abdication, something only further reinforced by one year in particular: 1936.
"The idea has always been that you do not give up your throne, you either live until you pass away, or you die on the battlefield," Swaby said.
"That's very much been the mantra of kings and queens in the past. So nobody's ever really put much thought into abdication."
That changed suddenly when Edward VIII abdicated in 1936 after 352 days so he could marry US divorcée Wallis Simpson.
"No one really knew what to do," Swaby said.
"And even though we have had an abdication, and it changed a lot, still nobody thought to make provisions for a future abdication.
"So all these questions are very much up in the air."
Swaby said other kings had abdicated or left the throne while still alive but he was the only one to do so willingly.
How is this different from Denmark?
The pressures on an ageing monarch aren't unique to Charles.
Denmark's Queen Margrethe became the first Danish monarch to abdicate in nearly 900 years in January when she handed over the throne to her son, Frederik.
Margrethe, 83, had always maintained she wouldn't quit.
But Britain isn't Denmark.
Queen Elizabeth II stuck by a commitment to devote her life to service before she died on the throne at the age of 96.
Charles made a similar commitment during his coronation.
What about a coronation?
If Charles was to abdicate in the near future, it would mean a second coronation in a couple of years for a British public that hadn't seen such a ceremony since a decade before The Beatles.
Swaby said she thought the next ceremony would likely be smaller than Charles' extravagant, albeit significantly stripped back, affair.
"I think some people only stomached King Charles' because we hadn't had one for 70 years because the queen had reigned for so long," she said.
"And if we do have one for William I think we'll see it be scaled back even more than we did for the King.
"So gradually if we do keep having them, they'll just get smaller and smaller every time."
In terms of timing, she expected it would likely fall in the summer and possibly somewhere in between Elizabeth's 16-month wait to be crowned and Charles' eight-month delay after accession.
What does this mean for Prince George?
You would think a little something like becoming the next in line to the throne would be a pretty big deal.
But Swaby said it would likely have a relatively limited impact on the young prince.
The King became the heir to the throne when he was three and a half, and he was pretty much bred to be king, his life has always been very constrained," she said.
"I don't think the Prince and Princess of Wales would let George's life be as constrained as the King."
What could happen if the King becomes too ill to work but doesn't abdicate?
While all the signals coming from the palace are positive, there are constitutional provisions in place if the King is unable to temporarily carry out his official duties.
In that instance, "counsellors of state" can be called upon to step in for him.
Two counsellors can be appointed to act on the monarch's behalf through what's known as a letters patent and help keep the state ticking over.
They would be authorised to sign documents, attend Privy Council meetings, and receive new ambassadors, but not perform some of the most important constitutional roles, such as appointing a prime minister.
The list of royals who can step in include Queen Camilla, Princes William, Harry and Andrew, and Princess Beatrice.
In 2022, the King expanded this pool of family members to include his siblings, Princess Anne and Prince Edward.
If this option was enacted over the coming weeks or months, it is unlikely the Dukes of Sussex or York would be directed to step up as they are no longer working royals.
What about a regency?
If the King becomes completely unable to carry out his constitutional duties and the state can no longer function properly, his powers can be withdrawn and assumed by a regent.
Under the Regency Act 1937, that would be the next in line to the throne, which is Prince William.
For that to happen, there has to be medical evidence "that the Sovereign is by reason of infirmity of mind or body incapable for the time being of performing the royal functions" or "is for some definite cause not available for the performance of those functions".
Who would make the decision?
At least three of five people need to be satisfied with the evidence by a majority vote to institute a regency.
That panel consists of the lord chancellor, the speaker of the House of Commons, the lord chief justice of England, the master of the rolls, and the Queen.
They would need to declare their decision in writing and would also declare if or when the King is ready to resume his duties.
In the meantime, Prince William would act in his name.
What would an abdication mean for Australia and the other realms?
In this case there is one big, if slightly technical, difference between a new monarch ascending the throne by abdication or demise.
That's because the UK's reigning monarch is also the head of state of Australia and 14 other Commonwealth countries, including Canada and New Zealand.
"I suppose this is one of the very few instances where the British government actually kind of decides the governance of other countries, because if he abdicates here, whilst the prime ministers of the realm countries need to be notified, they don't necessarily have a say over it," Swaby said.
"It's very much done here."
That decision becomes even more consequential in the event of a regency being instituted because House of Commons Speaker Lindsay Hoyle — an elected UK official — would be playing a direct role in choosing Australia's head of state.
- With Associated Press and CNN
