The Queen is set to miss the State Opening of Parliament for the first time in nearly 60 years.
Instead, the Prince of Wales will be reading the Queen’s Speech for the first time on Tuesday.
In a statement, Buckingham Palace said that the Queen continues to experience “episodic mobility problems”.
The Palace explained that in consultation with her doctors, she had “reluctantly decided” not to attend the State Opening.
It will be the first time that Charles has taken on a major constitutional duty of the head of state.
The Queen’s throne will remain empty in the House of Lords, whilst he and the Duchess of Cornwall will sit in their usual seats.
The State Opening of Parliament is the main ceremonial event of the parliamentary year.
For over 500 years, it has served as a symbolic reminder of the unity of Parliament’s three parts: the Sovereign, the House of Lords and the House of Commons.
The Queen’s Speech is written by the Government and sets out its agenda for Parliament’s new session.
A spokesman for Number 10 said: “The Prime Minister fully respects the wishes of Her Majesty and is grateful to the Prince of Wales for agreeing to deliver the speech on her behalf.”
The Queen is understood to have a busy diary at Windsor this week with a call with Australia undertaken on Monday, and a planned virtual Privy Council and phone audience with the Prime Minister on Wednesday.
She is expected to undertake some private engagements later in the week.
It would be only the third time during her reign that the Queen has not opened parliament – and the first time nearly 60 years.
The exceptions were in 1959 and 1963, when she was pregnant with Prince Andrew and then Prince Edward, when her speech was read by the Lord Chancellor.
The Queen has only been seen outside a royal residence or home on official duties once in the last seven months when she attended the Duke of Edinburgh’s memorial service in March, using a stick as she walked carefully to her seat.
Many of her light duties are now carried out by video calls, and the nation’s longest reigning sovereign remarked during a recent in-person audience: “Well, as you can see, I can’t move.”
The Queen spent a night in hospital in October undergoing tests and was then under doctors’ orders to rest for the next three months.
She missed the Remembrance Sunday Cenotaph service and Cop26 climate change talks last autumn.
The prince, the longest serving heir the throne in British history, has accompanied the Queen to the state opening on a number of occasions, and attended many times over the years.
But never has he delivered the Queen’s speech or opened parliament himself.