Saturday's parade -- which marks the sovereign's official birthday -- is a minutely choreographed military tradition dating back more than two centuries.

Charles's mother, Queen Elizabeth II, was the last monarch to ride at the event in 1986, when she was 60.

She decided after that to be driven in a carriage as Burmese, the horse she used for 18 years, was retired from duty.

The parade starts at Buckingham Palace in central London and moves down The Mall to Horse Guards Parade, where Charles, 74, will receive a royal salute.

He will then inspect soldiers on parade before returning with other members of the royal family to watch a ceremonial fly-past of aircraft from the palace balcony.

Charles, his only sister Princess Anne and heir Prince William, all rode at last year's Trooping the Colour.

It formed part of four days of celebrations for the late queen's Platinum Jubilee, marking her 70th year on the throne, and was one of her last public appearances before her death in September, aged 96.

Charles's younger son Prince Harry and his American wife Meghan kept a low profile at the event but have reportedly not been invited this year.

The couple moved to the United States in 2020 and have repeatedly criticised royal life since.

William reviewed troops on horseback in another military ceremonial Saturday. Temperatures of up to 28 Celsius (82 Fahrenheit) saw several soldiers faint.

Charles' actual birthday is on November 14.

The double birthday tradition was started by German-born King George II in 1748, who wanted to have a summer celebration as his own birthday was on October 30.