The Queen will not attend the State Opening of Parliament, Buckingham Palace has announced.
Her Majesty was due to deliver the traditional address, but less than 24-hours before the ceremony the decision was taken she would not attend - with Prince Charles set to read the Queen's Speech on her behalf.
It will be just the third time the Queen has missed event.
Buckingham Palace said in a statement: "The Queen continues to experience episodic mobility problems, and in consultation with her doctors has reluctantly decided that she will not attend the State Opening of Parliament tomorrow.
"At Her Majesty’s request, and with the agreement of the relevant authorities, The Prince of Wales will read The Queen's Speech on Her Majesty's behalf, with The Duke of Cambridge also in attendance."
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A new Letters Patent authorised by the Queen was issued to cover the State Opening delegating to Counsellors of State the royal function of opening a new session of Parliament.
In this instance, it enables Prince Charles and Prince William to jointly exercise that function. No other functions have been delegated by the Queen.
The Prince of Wales has previously accompanied the Queen to the State Opening of Parliament, but has never delivered the Queen's Speech.
The episodic mobility issues are said to be a continuation of the problems the Queen has suffered since the autumn.
She has been forced to pull out of a string of major engagements recently, missing both the Commonwealth Day celebration in March as well as the Maundy Day church service at St George's Chapel in Windsor.
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.
A No 10 spokesman 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."