The Queen will miss a thanksgiving service at St Paul's Cathedral tomorrow after experiencing "discomfort" at today's Platinum Jubilee celebrations, Buckingham Palace has confirmed.
The 96-year-old monarch, who has struggled with her mobility in recent months, made the decision "with great reluctance", officials said.
The service is being held on the second day of celebrations to mark her 70 years on the throne.
The Queen was pictured smiling alongside senior royals on the balcony at Buckingham Palace during the Trooping the Colour parade and flypast, but the day took its toll.
A source said that she experienced "episodic mobility issues", forcing her to make the "regrettable but sensible" decision not to attend tomorrow's service.
It is not known if the sovereign will miss any other events celebrating her seven decades as head of state.
A senior palace spokesman said: “The Queen greatly enjoyed today’s Birthday Parade and Flypast but did experience some discomfort.
“Taking into account the journey and activity required to participate in tomorrow’s National Service of Thanksgiving at St Paul’s Cathedral, Her Majesty with great reluctance has concluded that she will not attend.
“The Queen is looking forward to participating in tonight’s Beacon lighting event at Windsor Castle and would like to thank all those who made today such a memorable occasion.”
A royal source said: “Her Majesty enjoyed today immensely but episodic mobility issues were experienced during the course of the day
“A regrettable but sensible decision based on the journey, length of time involved and the physical demands a service at St Paul’s inevitably involve.
“It was always Her Majesty’s hope that she would attend rather than a firm commitment.”
It is the latest in a string of engagements which the Queen has been forced to miss due to health issues.
Last year she pulled out of a state visit to Northern Ireland and in October last year was admitted to hospital for her first overnight stay in eight years.
She also missed the Cop26 climate summit, the Festival of Remembrance and the Remembrance Sunday service at the Cenotaph.
Last month Prince Charles delivered the Queen's speech on her behalf at the State Opening of Parliament.
The Queen beamed as she kicked off her Platinum Jubilee celebrations by joining her family on the Buckingham Palace balcony for Trooping the Colour.
She chatted to her great-grandchildren Prince George, Princess Charlotte and Prince Louis as she stood alongside Prince Charles, the Duke and Duchess of Cambridge and other senior royals to watch the RAF flypast.
The famous balcony moment followed an impressive military parade, which Meghan Markle and Prince Harry were spotted watching through a balcony window having returned to the UK for the celebrations.
The Queen wore a dusky dove blue Charmelaine wool dress with pearl and diamante trim by Angela Kelly. She joined her cousin Duke to Kent to inspect the military parade before being joined by the rest of the family.
She used a walking stick and wearing the Guards' Badge on her coat.
Thousands of well-wishers have lined the Mall to mark the historic occasion, with some camping out overnight to secure the best seats in the house. The famous street is a sea of Union Jack flags, party hats, plastic tiaras and handmade signs bearing messages to the Monarch.
A new official photo of the Queen was released last night to mark the occasion, along with a message from the woman of the hour.
She said: "Thank you to everyone who has been involved in convening communities, families, neighbours and friends to mark my Platinum Jubilee, in the United Kingdom and across the Commonwealth.
"I know that many happy memories will be created at these festive occasions.
"I continue to be inspired by the goodwill shown to me, and hope that the coming days will provide an opportunity to reflect on all that has been achieved during the last seventy years, as we look to the future with confidence and enthusiasm."
