Britain put on a display of birthday pageantry Saturday for King Charles III with a military parade that also marked the Princess of Wales' first public appearance since her cancer diagnosis early this year.

The annual event was also a show of stability by the monarchy after months in which both the king and Kate, wife of the heir to the throne Prince William, have been sidelined by cancer treatment.

The 42-year-old princess traveled in a horse-drawn carriage from Buckingham Palace down the grand avenue known as the Mall with her children George, 10, Charlotte, 9, and 6-year-old Louis. Bystanders cheered as they caught a glimpse of Kate, dressed in a white dress by designer Jenny Packham and a wide-brimmed Philip Treacy hat.

Huge crowds turn out each June to watch the parade, also known as Trooping the Colour, which begins with a procession involving horses, musicians and hundreds of soldiers in ceremonial uniform from Buckingham Palace.

Prince William, in military dress uniform, rode on horseback for the ceremony, in which troops in ceremonial finery parade past the king with their regimental flag, or "colour."

Charles, who also is being treated for an undisclosed form of cancer, traveled in a carriage with Queen Camilla, rather than on horseback as he did last year.

The king inspected the troops from a dais on the parade ground, saluting as elite regiments of Foot Guards marched past.

Five regiments take turns to parade their colour, and this year it was the turn of a company of the Irish Guards, which has Kate as its honorary colonel. The troops, dressed in scarlet tunics and bearskin hats, were led onto the parade ground by their mascot, an Irish wolfhound named Seamus.

After the parade, members of the family went to a Buckingham Palace balcony to watch a fly-by of military aircraft — and delight the crowds below. 

In one of the many quirks of British royal convention, Saturday is not the king's real birthday — that's in November. Like his mother Queen Elizabeth II before him, Charles has an official birthday on the second Saturday in June. The date was chosen because the weather is generally good, though early sunshine on Saturday gave way to a blustery, rainy day in London.

In:
• King Charles III
• British Royal Family
• Prince William Duke of Cambridge
• Kate Duchess of Cambridge
• United Kingdom