The Royal Family kick off Queen's Platinum Jubilee celebrations with Trooping the Colour

The Queen has suddenly pulled out of her Jubilee thanksgiving service at St Paul’s Cathedral after being stricken with pain during today’s festivities.

The news comes after Her Majesty Queen Elizabeth II was joined by members of the royal family to watch the Trooping the Colour — a military parade that has marked each sovereign's official birthday since 1760.

Her Majesty, 96, is said to have taken the decision with "great reluctance" after suffering "discomfort" while watching a 70-aircraft RAF flypast on the balcony of Buckingham Palace while cheered by crowds of fans.

In recent months the monarch has been suffering "episodic mobility problems" in the weeks leading up to this week’s four-day celebration of her 70-year reign.

In a statement, Buckingham Palace said: "The Queen greatly enjoyed today’s Birthday Parade and Flypast but did experience some discomfort."

During the event, Elizabeth appeared to bask in her moment. Smiling, she chatted with her great-grandson Prince Louis, 4, who occasionally covered his ears as 70 military aircraft old and new swooped low over the palace to salute the Queen. The six-minute display included a formation of Typhoon fighter jets flying in the shape of the number 70.

The Queen, wearing a dusky dove blue dress designed by Angela Kelly, was joined on the balcony by more than a dozen royals — though not Prince Harry and his wife Meghan, who gave up front-line royal duties two years ago. The couple travelled to London from their home in California with their two young children to take a low-key part in the celebrations and watched the Trooping the Colour with other members of the family.

The jubilee is being commemorated with a four-day holiday extravaganza and events including a concert at Buckingham Palace on Saturday and a pageant staged by thousands of performers drawn from schools and community groups around the country on Sunday. Thousands of street parties are planned nationwide, repeating a tradition that began with the Queen's coronation in 1953.

In a written jubilee message, the Queen thanked people in Britain and across the Commonwealth involved in organising the celebrations. This country does like a good party.

"I know that many happy memories will be created on these festive occasions," Elizabeth said. "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 70 years, as we look to the future with confidence and enthusiasm."

Congratulations arrived from world leaders, including US President Joe Biden and Pope Francis. French President Emmanuel Macron called Elizabeth "the golden thread that binds our two countries" and former US President Barack Obama recalled the Queen's "grace and generosity" during his first visit to the palace.

"Your life has been a gift, not just to the United Kingdom but to the world," Obama said in a video message, adding: "May the light of your crown continue to reign supreme."

In a statement, Buckingham Palace said: "The Queen greatly enjoyed today’s Birthday Parade and Flypast but did experience some discomfort."

It is understood the Queen will still attend tonight's beacon lighting event.

The palace added: "Taking into account the journey and activity required 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 beacon consisting of more than 2,000 torches across the UK and the Commonwealth will be lit tonight to honour her seven decades on the throne.

The thanksgiving service will be the biggest royal outing of the Jubilee and it is thought all other senior royals will attend.

They include Prince Harry, 37, his wife Meghan, 40, and the couple’s two children Archie, three, and Lilibet – who turns one on Saturday.

It emerged earlier this week the Queen was not expected to attend Saturday's Derby – one of her favourite events of the year – and is believed to have chosen to watch on the television.

This article was first published by the NZ Herald and is republished here with permission, additional reporting by The Hits and Bang! Showbiz