Currently, if Charles is unable to carry out his duties due to "illness of absence abroad", one of the Counsellors of State is able to step in for him.
Under the 1937 Regency Act, all Counsellors of State are the four highest candidates in the royal line of succession who are over the age of 21, at the moment they are: Prince William, Prince Harry, Prince Andrew and Princess Beatrice.
The King's wife, Queen Consort Camilla, is also able to fill in for Charles, even though she is not in the line of succession.
However, Charles reportedly wants to change the rules, making it so that only working royals can be Counsellors of State, meaning Harry, Andrew and Beatrice would be knocked out, the UK's Daily Telegraph reports.
The King has always wanted to 'slim down' the royal family and this change could mean Princess Anne and Prince Edward are made the new Counsellors of State.
Charles may even choose to have the law rewritten altogether, allowing Kate Middleton, who is not in the line of succession, to become one of the Counsellors.
"It is believed that the King recognises the incongruity of having a trio of non-working Royals able to step into his shoes if he is abroad or incapacitated," the Telegraph noted.
The publication adds that Charles will likely have the "law changed as soon as he can".
Any changes that take place will be enacted by the Houses of Parliament.
The Queen previously had the law changed in 1953 to allow Prince Philip to act as Regent, if one of their children were to become king or queen before they turned 18.
Harry 'devastated' by ban
It comes after Harry was left "devastated" after having the Queen's initials, ER, removed from his military uniform for a vigil over the Queen's coffin in Westminster Hall on Saturday alongside the Queen's other grandchildren.
The initials were removed as he is no longer a working member of the royal family, however, Prince Andrew was allowed to keep them despite no longer being a working royal.
Harry was reportedly so "heartbroken" by the ban that he considered ditching his military uniform altogether, according to the Sunday Times.
The initials are only to be worn by those "in service" of the monarch.
"He is heartbroken," a friend told the publication. "To remove his grandmother’s initials feels very intentional."
Harry was given special permission to wear his military uniform for the vigil despite previously being banned after Andrew was also given permission to wear his during the Vigil of the Princes.
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