What to know as King Charles takes part in his first Trooping the Colour birthday parade as monarch

King Charles III rode on horseback Saturday to take part in his first Trooping the Colour ceremony as monarch, inspecting hundreds of soldiers and horses in a spectacular annual military display at central London's Horse Guards Parade.

Charles, 74, the colonel in chief, received the royal salute and watched as the most prestigious regiments in the U.K. army paraded to mark his official birthday.

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It was the first time in more than 30 years that a U.K. monarch has taken part in the pomp-filled ceremony on horseback.

Earlier, Charles' eldest son, Prince William, and the king's siblings, Prince Edward and Princess Anne, also rode on horseback in procession from Buckingham Palace. All the royals were dressed in red and gold tunics and tall black bearskin hats, matching the uniforms worn by many of the 1,400 soldiers taking part.

Others in the royal family, including Queen Camilla, Kate, the Princess of Wales, and her three young children, rode in horse-drawn carriages as thousands of people thronged the Mall, the grand avenue outside Buckingham Palace, to watch the pageantry.

Here are some things to know about the colourful spectacle:

BIRTHDAY PARADE

Trooping the Colour is essentially a grand birthday parade to honor the reigning monarch. The annual ceremony is a tradition that dates back more than 260 years.

Huge crowds turn out each June to watch the display, which begins with a procession involving horses, musicians and hundreds of soldiers in ceremonial uniform from Buckingham Palace. The monarch then inspects their troops, including both foot guards and horse guards. Gun salutes and a crowd-pleasing military flyby over the palace typically round out the celebrations.

Charles' actual birthday is Nov. 14, 1948. But U.K. monarchs have traditionally celebrate two birthdays -- their real one and an official one -- to ensure that public celebrations can take place in warm summer weather.

Charles' late mother, Queen Elizabeth II, always held the Trooping the Colour birthday parade in June, while she celebrated her actual April birthday privately with family.

"THE COLOUR"

The central part of the parade features a battle flag -- or the "Colour" -- being displayed and marched past troops and the monarch.

This is a ceremonial reenactment of the way regimental flags were once displayed for soldiers on the battlefield to provide a crucial rallying point if they became disoriented or separated from their unit.

The flags were traditionally described as "Colours" because they displayed the uniform colours and insignia worn by soldiers of different units.

A different flag is trooped each year. This year the "Colour" was the King's Colour of the 1st Battalion Welsh Guards.

KING ON HORSEBACK

Saturday was the first time a monarch has ridden on horseback at the event since Elizabeth did so in 1986.

The queen rode her favorite horse, called Burmese, to 18 Trooping the Colour ceremonies until the black mare retired in 1986. After that she decided to use a carriage for the event instead.

Charles also rode on horseback for the spectacle last year, when as heir to the throne he inspected the troops on behalf of his mother. Elizabeth died last September at the age of 96.

BONUS MILITARY FLYBY

The birthday parade typically reaches its climax when, at the end of the military procession, the royal family lines up on Buckingham Palace's balcony to watch a spectacular flyby.

The Royal Air Force's aerobatic team, the Red Arrows, usually wows the crowds as they fly in formation leaving plumes of red, white and blue vapor trails.

This year, the flyby was even more impressive, because a similar display on Charles' coronation day in May had to be scaled back because of bad weather. Around 70 aircraft took part Saturday, including Spitfire and Hurricane fighters from the Battle of Britain Memorial Flight.

Eighteen Typhoon fighter jets flying in precise formation spelt out "CR" -- "Charles Rex" -- in the sky as the royal family and thousands of spectators cheered.