The tradition of this parade, known as "Trooping the Colour", dates back to the reign of George II in 1748, who, although born on 30 October, wanted to take advantage of the good weather to celebrate his birthday.
ADVERTISEMENTKing Charles III reviewed the troops on Saturday morning in his first birthday parade as monarch, which he performed on horseback, a first for a monarch since 1986.
Held every June, the parade marks the official birthday of the King, who turns 75 on 14 November and will then celebrate the occasion in private.
Under cloudy skies, Charles III left Buckingham Palace in procession shortly after 10:30 am local time, followed by his brother Prince Edward and his sister Princess Anne, as well as his son and heir to the throne William, all three of whom were also on horseback.
Queen Camilla, Princess Kate and her three children - George, Charlotte and Louis - followed in a carriage.
The tradition of this parade, known as "Trooping the Colour", dates back to the reign of George II in 1748, who, although born on 30 October, wanted to take advantage of the good weather to celebrate his birthday.
The event is televised and always attracts large crowds to the area around Buckingham Palace where the parade takes place.
Queen Elizabeth II, who died last September at the age of 96, had not appeared in the saddle at this emblematic event of British royal pomp since 1986.
Some 1,400 soldiers, 400 musicians and 200 horses took part in the ceremony, which was held in Horse Guards Parade Square in central London.
The mare Juno led the parade, followed by three drum horses - Perseus, Atlas and Apollo. These equines, which carry the drums during parades, are the most experienced animals in the British armed forces. They have the rank of major and are named after figures from Greek mythology.
Balcony and cannon fire
This ceremony has its origins in the preparations for war, when all the flags were shown to the soldiers so that they could recognise them in the confusion of battle.
The First Battalion of the Welsh Guards is being honoured this year, and after inspecting the troops, Charles III, who as Head of State is Commander-in-Chief of the Armed Forces, will lead the procession back to Buckingham Palace.
Joined by Queen Camilla and other serving members of the Royal Family, the King will greet the crowds from the Palace balcony and watch an aerial parade after 41 cannon shots fired from Green Park.
This year, the parade of 70 aircraft will be larger, to compensate for the cancellation of the parade planned for the King's coronation on 6 May, which was disrupted by bad weather.
The King's birthday celebrations are the occasion, along with the New Year, for the announcement of honours and decorations for personalities and individuals.
This year's list includes novelist Martin Amis, who died last month, film director Stephen Frears, Vogue editor Anna Wintour, and Junior Frood, an 18-year-old student who became a campaigner against bullying at school after being bullied.