Queen Elizabeth's son and heir Prince Charles and her grandson Prince William will pay tribute to the record-breaking monarch at a pop concert at Buckingham Palace on the third day of nationwide celebrations for her 70 years on the throne.
The "Party at the Palace," which will feature singers Alicia Keys and Diana Ross, is the main Platinum Jubilee event Saturday.
By early evening, tens of thousands of people had gathered on the Mall, the grand boulevard that runs up to the palace, and in a nearby park to watch the concert on big screens, while those with tickets surrounded the stage on a warm evening.
The 96-year-old monarch was not present, having missed a number of Jubilee events because of "episodic mobility problems" that have caused her to cancel engagements recently.
Other acts to appear include rock band Queen + Adam Lambert, singer Rod Stewart and veteran U.S. musician Nile Rodgers. Elton John recorded a special performance.
Queen guitarist Brian May, who played the national anthem from the roof of the palace at a concert for Elizabeth's golden jubilee in 2002, hinted at another memorable moment.
"There was a moment when I wondered ... after Buckingham Palace roof where can you go? Well ... you will see," he said.
Andrew Singleton, a 56-year-old window fitter from northern England who was in the queue for the concert, said the Jubilee had helped to bring the country together.
"People have traveled from as far as America to actually come here and just enjoy the celebrations," he said.
Earlier in the day the queen also missed the Epsom Derby horse race.
Her daughter Princess Anne, who competed in the three-day equestrian event in the 1976 Olympics, stood in for her mother, who has rarely missed the race during her record-breaking reign and watched on television from her Windsor Castle home.
Four days of celebrations to mark the monarch's 70 years on the throne began with a military parade, a Royal Air Force fly-by, and the lighting of beacons across Britain and the world, with tens of thousands of people joining the festivities.
During Friday's National Service of Thanksgiving at St Paul's Cathedral in London, Archbishop of York Stephen Cottrell used a horse racing analogy in his sermon to pay tribute to the queen.
"Your Majesty, we are sorry that you're not here with us this morning, but we are so glad that you are still in the saddle," he said. "And we are glad that there is still more to come. So, thank you for staying the course."
A sideshow to the main celebrations has been Prince Harry and his American wife Meghan making their first public appearance together in Britain since quitting official duties to move to Los Angeles two years ago, during which time their relationship with other royals has become strained.
Notably Saturday, the official Twitter accounts for the monarch, Charles and William all sent messages almost simultaneously to mark the first birthday of Lilibet, the couple's daughter who is named after the queen.
Elizabeth had not met her great-granddaughter before the trip, and Buckingham Palace has not commented on newspaper reports that they have finally been introduced.
Harry and Meghan have become divisive figures, with supporters regarding them as a breath of fresh air for the tradition-bound monarchy, while critics and many newspapers pour scorn on their commercial activities such as striking a deal with global streaming service Netflix.
"So Far Apart," the Daily Mail newspaper said on its front page about the lack of any obvious interaction between Harry and elder brother William at Friday's thanksgiving service.