History is littered with young monarchs being guided by slightly dubious stewards because they were too young to reign alone.
Well, when it came to the surprise appointment of King George VI (his brother, King Edward VIII, had abdicated to marry an American divorcee), it was decided to formally put the rules into law.
That came in the form of the Regency Act in 1937.
It exists to allow someone else to rule in a monarch's stead in the event they are not yet an adult, or have become incapacitated.
There have been calls to update the legislation in recent years due to changes in the Royal Family.
What is the Regency Act?
The Regency Act 1937 lays out who stands in for a monarch in a range of situations if they cannot exercise their functions.
It came in during the first year of the reign of King George VI. The reluctant sovereign’s heir was his 10-year-old daughter, Elizabeth.
She would go on to become the longest-reigning British monarch in history, having taken to the throne at the age of 25 following the death of her father in 1952.
But, before then, there were fears about, should her father have died before she reached the age of 18, who would step in as regent to act in her place until she was an adult.
What happens if King Charles falls ill?
The 85-year-old law sets out the circumstances in which a “regent” — someone to rule in the monarch’s stead — can be appointed.
The first such circumstance where the act allows intervention is in the event of an underage monarch.
If the throne passes to someone aged under 18, then a regent is appointed to rule for them until they reach adulthood.
The second circumstance is the incapacity of the monarch.
If it is decided that they cannot carry out their functions, a regent is appointed until the king or queen is deemed capable of taking on their responsibilities again.
When the Queen’s health issues came to light, particularly when she missed the State Opening of Parliament in May — only the third time during her seven-decade rule that she missed the occasion — there was talk that the 96-year-old might have wanted to invoke the Act.
The Queen was reportedly said to be considering whether to appoint the then-Prince of Wales to take over her responsibilities due to her mobility issues and increasing frailty.
She died on September 8, however, without deploying the act, with her heir automatically becoming King Charles III.
Who can be regent?
In its most simple interpretation, the Regency Act states that the next adult in the line of succession is regent, providing they are a British subject and resident in the United Kingdom.
As it currently stands, King Charles’ regent would be his eldest son, William, the new Prince of Wales.
If William becomes king before his children reach adulthood, then, by law, his regent would be Harry, the Duke of Sussex.
However, there are calls for the Act to be amended due to the fact Harry has stepped down as a working royal and is residing in California. He would likely have to return to the UK should he be appointed regent.
The next adult in line to the throne after Harry is Prince Andrew, the Duke of York, who has also stopped being a working royal following a controversial US sexual assault case against him that was settled earlier this year.
Should he be skipped over as regent as well, then responsibility would fall to Andrew's eldest daughter, Princess Beatrice, who is ninth-in-line to the throne.
How does the Regency Act affect Prince George?
Should there be tragic circumstances that mean Prince George, aged nine, ascends to the throne before he is 18, then the Regency Act would come into play.
Prince Harry continues to be the next adult in line to the throne after George, meaning he would take over regency duties (pending his move back from the US).
However, the guardianship of a monarch under the age of 18 rests with their surviving parent, meaning the Princess of Wales would continue to have control over his upbringing.
Guardianship of a ruler declared incapable, possibly due to old age, rests with their spouse, if they have one. In this case the role would fall to Camilla, Queen Consort.
