The monarch, 96, has pulled out of the major ceremonial occasion because she is suffering from “episodic mobility problems”. Her doctors have advised her not to attend.
The Prince of Wales will read the queen’s speech for the first time, which will be interpreted as a significant shift in his responsibilities as a king in waiting.
The Duke of Cambridge, also a future monarch, will attend the occasion for the first time.
The queen’s throne will remain empty in the House of Lords. The Prince of Wales and the Duchess of Cornwall, who is also attending, will sit in their usual seats.
Prince William will sit on the opposite side of his father to Camilla.
The state crown will still travel to Parliament.
“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,” said Buckingham Palace.
“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.”
No other functions have been delegated.
The mobility issues are said to be a continuation of the problems Queen Elizabeth has suffered since the autumn.
“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,” said a Number 10 spokesman.
The queen is understood to have a busy diary at Windsor this week, with a call with Australia undertaken on Monday, and a planned online 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 Queen Elizabeth has not opened Parliament – and the first time in nearly 60 years.