A pop concert, featuring the likes of singers Alicia Keys and Diana Ross, and the Epsom Derby horse race take centre stage on the third day of Britain's nationwide celebrations for Queen Elizabeth's Platinum Jubilee.
However, the 96-year-old monarch, a huge horse-racing fan and owner of many thoroughbreds, will skip the 243rd running of the Derby because of "episodic mobility problems" which also forced her to miss a thanksgiving service in her honour on Friday.
Her daughter Princess Anne, who competed in the three-day equestrian event in the 1976 Olympics, is expected to stand in for her mother.
Later on Saturday, performers from around the world will entertain some 22,000 people at the "Platinum Party at the Palace", while Elizabeth's son and heir Prince Charles and grandson Prince William will speak.
The queen herself had not been expected to attend.
The concert will also feature a specially recorded performance by Elton John, a performance from rock band Queen + Adam Lambert, and conclude with Diana Ross' first live appearance in Britain in 15 years.
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, said the band was happy to have been invited again.
"Then there was a moment when I wondered ... after Buckingham Palace roof where can you go? Well ... you will see," he said.
Four days of celebrations to mark the monarch's record-breaking 70 years on the throne began with a military parade, a Royal Air Force flypast, and the lighting of beacons across Britain and the world.
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."