Britain's King Charles III Charles inspected the troops at his inaugural birthday parade on horseback Saturday, the first time the monarch has ridden at the event since his mother, Queen Elizabeth II, in 1986.
The annual Trooping the Colour parade marks the British sovereign's official birthday.
Charles was followed on horseback by his eldest son and heir, Prince William, Charles' brother Edward, the Duke of Edinburgh, and sister Anne.
Queen Camilla and William's wife Catherine, the Princess of Wales followed in a carriage.
The colourful display of regimental precision and pageantry is the first of 74-year-old Charles's reign.
Charles's actual birthday is on November 14 but British sovereigns celebrate twice -- once in private and again in public.
The June parade tradition began in 1748 under King George II, who wanted a celebration in better summer weather, as his own birthday was on October 30.
The televised event kicked off with a procession from Buckingham Palace to Horse Guards Parade in central London.
Some 1,400 soldiers, 400 musicians and 200 horses are taking part, led in the parade by Juno, a 10-year-old shire mare, alongside three other Drum Horses -- Perseus, Atlas and Apollo.
Drum Horses are the most senior animals in the army and hold the rank of major. They are traditionally named after figures from Greek mythology.
The minutely choreographed event has its origins in the display of colours or flags of different regiments to allow their soldiers to identify them in battle.
The 1st Battalion Welsh Guards will troop, or parade, their colour up and down the ranks this year.
The UK is currently experiencing a hot spell making it difficult for the troops in their ceremonial black bearskin hats and thick red tunics.
William inspected troops from the Household Division group of senior regiments last weekend, and the high temperatures saw several soldiers faint.
As Prince of Wales, William is honorary colonel of the Welsh Guards.
Charles -- who as head of state is commander-in-chief of the armed forces -- will later lead soldiers back to the palace.
He will then join other senior members of the royal family to watch a fly-past of some 70 military aircraft over the British capital, after a 41-gun salute from nearby Green Park.
Bad weather cut short a planned fly-past at Charles's coronation on May 6.
The late Queen Elizabeth last rode her horse Burmese, a gift from the Royal Canadian Mounted Police, at the parade in the mid-1980s.
After the horse, which she rode for 18 years, was retired in 1986 she decided to use a carriage for Trooping the Colour.
Last year's parade was the last for the late queen, and formed part of four days of events to mark her record-breaking 70th year on the throne.
It was one of her final public appearances before her death, aged 96, in September.