The King is being treated for cancer, the sovereign's health problems have raised questions about whether there may be a need for a regency in the future.
If Charles were incapacitated, the Prince of Wales could be appointed Prince Regent through the Regency Act 1937, taking over the functions of the King.
However, Prime Minister Rishi Sunak said the king's cancer was “detected early”, suggesting any prospect of a regency is unlikely at this stage.
If necessary, it would be the first time in more than 200 years that the British monarchy would require a regency, with the last Prince Regent being the future George IV.
Here is an explanation of what a regency means and how and why it would occur:
What is a regency?
A period of regency allows the king to transfer his powers as monarch to the Prince of Wales without having to abdicate.
Does this mean William would be king?
No. The king would still be the monarch and head of state.
But William would be able to act real operates in the name and on behalf of Charles.
What would lead to a regency?
The Regency Act 1937 states that the monarch's duties will be performed by a regent if the monarch is declared “by reason of infirmity of mind or body” unable to perform real functions, or if there is “evidence that the Sovereign, for some defined reason, is not available to perform these functions”.
This must be declared in writing by three or more of the following: the sovereign's wife, the Queen, the Lord Chancellor, the Speaker of the House of Commons, the Lady Chief Justice and the Master of the Rolls.
Charles has no voice and does not need to agree with their decision.
Why wouldn't the king abdicate?
The abdication of the late queen's uncle, Edward VIII, in 1936 triggered a major constitutional crisis and the royal family has never forgotten its devastating impact.
The king made a “pledge of lifelong service” in his first address to the nation when he became monarch.
Why couldn't the king just walk away?
The British monarchy is also a priestly monarchy – as part of his coronation, the king underwent a consecration ritual that is similar to the consecration ritual that a priest goes through.
You may stop being an active priest, but you will remain a priest until you die.
Edward VIII abdicated before being crowned.
Why couldn't William simply act as a Councilor of State?
A regency is a longer term solution than temporary State Councilors.
But State Counselors cannot perform certain fundamental constitutional functions, such as Commonwealth matters, the dissolution of parliament except on the instruction of the King, the creation of peers and the appointment of a prime minister.
Charles and William jointly held the state opening of parliament in place of the late Queen as Counselors of State in 2022.
Is a regency a permanent arrangement?
No. It is reversible. If a monarch's health recovers or he becomes available to carry out his real functions, the sovereign can resume his duties.
Who was the last Prince Regent?
The last regent was the future George IV, who became Prince Regent through an ad hoc Regency Act in 1811, when his father, George III, was declared mentally unfit to be king.
The vain Prince Regent, famously played by Hugh Laurie in the sitcom Blackadder III, was known for his intoxicating extravagance, which was a constant source of gossip.
He was an important artistic patron, acquiring an impressive art collection and sponsoring architects and designers, and later commissioned the Real Pavilion in Brighton will be built as his seaside pleasure palace.
He was regent for nine years before becoming king when his father died in 1820.
Are there already laws in place for modern rule?
Yes. Permanent provisions were implemented through the Regency Act passed in 1937 in the event of a monarch becoming incapacitated or a sovereign being under 18 years of age.
Princess Elizabeth was heir to the throne and was just 11 years old in 1937.
Further Regency Acts were also passed in 1943, and later in 1953, to allow Prince Philip, the late Duke of Edinburgh, to be regent if necessary and the Queen's children were under 18.
But future changes to the legislation may be necessary because the second in line to the throne, Prince George, is under 18 years old.
Options could include adding the Princess of Wales to the Regency Bill as a potential regent should something happen to Charles and William before George became an adult.
How is a regency established?
A declaration must be made to the Privy Council and communicated to the Government.
William would have to take an oath before the Privy Council, in which he pledged to be faithful and give true loyalty to the king, to faithfully execute the office of regent and to govern in accordance with the law, and to preserve the Church of Scotland.
Is there any limit to what William could do as Prince Regent?
Yes. He would not be allowed to give assent to any bill that would alter the order of succession to the throne.
He would also not be permitted to repeal or amend a law made in Scotland entitled “An Act to Protect the Protestant Religion and Government of the Presbyterian Church.”
The Act of 1707 guaranteed in the pre-Union Parliament of Scotland that the status of the Church of Scotland would not be affected by Union with England.
Would the prince be the Prince Regent of the other 14 nations where the King is head of state?
No. Constitutional expert Professor Vernon Bognador previously said it would be up to these countries to take their own action.