The Queen has given her son Prince Charles an "unofficial elevation" to be her regent "in all but name" according to royal sources.
This would effectively remove Prince Harry and Prince Andrew from being able to take part in official duties in their roles as Counsellors of State.
This comes as the Queen has pulled out of attending the Royal Maundy church service, for the first time since 1970.
Her Majesty will be represented for the first time by the Prince of Wales and Duchess of Cornwall, Buckingham Palace has announced.
The Prince of Wales will attend the Royal Maundy church service.
Phil Noble
Prince William and Prince Harry are both Counsellors of State
Yui Mok
The annual event is an important fixture in the royal calendar and will see Charles follow the ancient tradition of distributing Maundy money to community stalwarts on Thursday.
It is understood the Queen, who has been experiencing mobility issues, was unable to commit to the event and, with the order of service being printed, she was keen for the arrangements to be confirmed to avoid any misunderstanding or the day to be overshadowed.
The Ephraim Hardcastle column in the Daily Mail said: "We have effectively a co-monarchy for the first time since William and Mary arrived in 1689.
"Charles's unofficial elevation also removes any danger of Andrew or Harry having to step in as Counsellors of State."
The website explains the responsibilities of a Counsellor of State: “in the event that The Queen cannot undertake her official duties as Sovereign on a temporary basis due to illness or absence abroad, two or more Counsellors of State are appointed by Letters Patent to act in Her Majesty's place.”
After the death of Prince Philip in April 2021, the next four Counsellors of State are Prince Andrew, Prince Charles, Prince William and Harry.