King Charles III will mark the first official birthday of his reign on horseback, restoring a royal tradition that dates back more than two and a half centuries.
From his horse the king, 74, will take the salute from troops at the annual Trooping the Colour parade on Saturday in central London, becoming the first monarch in more than 30 years to do so.
His mother Queen Elizabeth II was the last monarch to ride at the event in 1986, when she was 60.
Trooping the Colour through the years – in pictures
The meticulously choreographed military tradition celebrates the sovereign's official birthday, a custom started by German-born King George II in 1748, who wanted a summer celebration as his own birthday was on October 30. The current king's actual birthday is on November 14.
Thousands gathered at Horse Guards Parade to witness the Colonel's Review at the weekend, a rehearsal, with Prince William inspecting the troops on horseback. At least three soldiers fainted in the heat.
The ceremony involved hundreds of horses and soldiers carrying out complex battlefield drill manoeuvres to military music.
But with temperatures reaching 28°C, the heat proved too much for some and the prince later tweeted his thanks to those who had taken part.
“Conducting the Colonel's Review of the King's Birthday Parade today. The hard work and preparation that goes into an event like this is a credit to all involved, especially in today’s conditions,” he wrote.
What is Trooping the Colour?
The annual event has marked the official birthday of the sovereign for more than 260 years.
Queen Elizabeth II last took part in the parade on horseback in 1986, when she rode her favourite steed, a black mare called Burmese, for the 18th and final time in the annual ceremony before it was taken to Windsor for retirement.
The queen decided that rather than train another horse for the ceremony, she would in future be driven in a carriage.
In 1981, the queen was riding Burmese at the Trooping the Colour parade when Marcus Sarjeant fired blank shots at her while she was riding along The Mall. The former Royal Canadian Mounted Police horse began to rear in fright but the queen, an accomplished equestrian, quickly brought the horse back under control.
Sarjeant was sentence to five years in jail.
King Charles, his only sister Princess Anne and heir to the throne Prince William all rode at last year's event.
The parade formed part of four days of celebrations for the late queen's platinum jubilee, marking her 70th year on the throne. It was one of her last public appearances before her death in September, aged 96.
What will happen on Saturday?
The parade starts at Buckingham Palace in central London and moves down The Mall to Horse Guards Parade, where Prince Charles will receive a royal salute.
He will then inspect soldiers on parade before returning to watch a ceremonial fly past of aircraft from the palace balcony.
The monarch will be joined by his wife Queen Camilla and members of the royal family to watch the 1st Battalion Welsh Guards troop their colour, with the sovereign's escort provided by the Life Guards and the Blues and Royals.
When does it start?
The parade begins at 10am.
Who will be there?
Many members of the royal family are expected to attend, including Queen Camilla and the Prince and Princess of Wales.
Prince Charles's younger son Prince Harry and his wife Meghan have reportedly not been invited this year.
How can I see it?
It is possible to watch the event in person but it will also be televised.
For those who do travel into central London to see the parade, members of the public are advised to stand on The Mall or on the edge of St James's Park, overlooking Horse Guards Parade, from 9am.