Prince Charles is to read the Queen’s Speech on her behalf for the first time, after the 96-year-old monarch pulled out due to mobility problems.
Prince William will accompany his father to open Parliament after the Queen granted special permission.
The Queen’s Speech is a ceremonial occasion which sets out laws the government wants to pass and highlights its priorities for the months ahead.
It is the first time since 1963 that the Queen will not deliver the speech.
At that time, she was pregnant with Prince Edward, and it was instead read by the Lord Chancellor.The monarch also bowed out of delivering the speech in 1959 while pregnant with Prince Andrew.
It will be Prince William’s first state opening, and he and Prince Charles will be accompanied by the Duchess of Cornwall.
The Queen’s main throne will remain empty in the House of Lords on Tuesday but the Imperial State Crown – traditionally worn by the monarch at the event – will still travel to Parliament.
A rule change known as a Letters Patent was authorised by the monarch to delegate the opening of Parliament after it was decided on Monday that Prince Charles would take the Queen’s place.
Prince Charles and Prince William are counsellors of state – the category of royal that includes the next four people in the line of succession who are over the age of 21.
Buckingham Palace said on Monday that the decision to pull out had been taken in consultation with the Queen’s doctors, as she continues to experience “episodic mobility problems”.
The Palace said in a statement: “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.”