The Queen will not attend Friday’s Jubilee service at St Paul’s Cathedral after experiencing discomfort while watching Thursday’s parade at Buckingham Palace.
The decision was made with “great reluctance” after considering the “journey and activity required”, the palace said.
However, she did take part in a beacon lighting ceremony on Thursday evening.
Four days of celebrations marking the Queen’s 70-year reign began earlier.
The 96-year-old monarch appeared twice at Buckingham Palace balcony, flanked by other senior royals, as they watched a military parade and waved at thousands of well-wishers gathered on The Mall.
Hours after the ceremony, the palace confirmed she would not attend Friday’s thanksgiving service, but said she “would like to thank all those who made today such a memorable occasion”.
The service at St Paul’s in central London will give thanks for the Queen’s seven decades as monarch.
Senior royals including the Prince of Wales, Duchess of Cornwall and the Duke and Duchess of Cambridge will all attend, with Prince Charles officially representing the Queen.
The Duke and Duchess of Sussex – who have flown over from California – will also join. It will be Prince Harry and Meghan’s first royal event together since leaving the UK two years ago.
However, Prince Andrew will be absent after testing positive for Covid.
The royals will be joined by more than 400 honours recipients, including NHS and key workers, public servants and representatives from charities and the Armed Forces.
Prime Minister Boris Johnson will give a reading from the New Testament.
The largest church bell in the UK, the 16-tonne Great Paul, will ring continuously for four hours after the service. The event begins at 11:30 BST on Friday, with coverage starting on BBC One from 09:15.
Thursday evening’s beacon lighting event saw the Queen symbolically touch a globe to begin the ceremony at Windsor Castle.
The head of state illuminated the globe, symbolically sending a chain of lights from her Windsor Castle home to Buckingham Palace, where Prince William watched as a sculpture, the Tree of Trees, was bathed in light.
The service is not the first engagement the Queen has had to miss in recent weeks because of health problems.
In May, she missed the State Opening of Parliament because of “episodic mobility problems” and in February she caught Covid, which she said left her feeling “very tired and exhausted”.
by Sean Coughlan, royal correspondent
The Queen will have pulled out of the thanksgiving service only with very great regret.
She has a deep religious faith and the service at St Paul’s Cathedral would have been one of her highest priorities for the weekend.
It was thought that she was more committed to attending the church service than many of the weekend’s events.
But Thursday’s exertions have left her suffering from discomfort, with a recurrence of the mobility problems that have caused her to cancel events before.
Now it seems the journey to St Paul’s, a procession and the length of the church service have become too difficult.
It’s at short notice, with the programme for the church service already printed. So it will leave a real sense of loss to have the Queen, the focal point of the service, no longer attending.
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