Princess of Wales attends Trooping the Colour for King Charles III's birthday

It is her first public appearance since her cancer diagnosis

The Princess of Wales, Prince George, Princess Charlotte and Prince Louis attend the Trooping the Colour parade in London to honour King Charles III's official birthday. Reuters

Catherine, the Princess of Wales, has made her first public appearance since her cancer diagnosis at the Trooping the Colour celebration to mark King Charles III's birthday.

Crowds of people gathered outside Buckingham Palace in London on Saturday for the military parade, with many holding Union flags.

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

The princess announced on Friday that she would attend the King's Birthday Parade after making progress in her treatment.

She disclosed in March that she was undergoing chemotherapy for an unspecified form of cancer.

“I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days,” she said in a statement, adding that she faces “a few more months” of treatment.

The 42-year-old princess is expected to travel by horse-drawn carriage from Buckingham Palace with her children George, 10, Charlotte, nine, and six-year-old Louis. She will watch the ceremony from a building overlooking Horse Guards Parade, a ceremonial parade ground in central London.

Prince William will be on horseback for the ceremony, in which troops in full dress uniform parade past the king with their regimental flags.

The king, who also is being treated for an undisclosed form of cancer, is due to inspect the troops alongside Queen Camilla from a carriage.

He disclosed his cancer diagnosis in February, and has recently eased back into public duties. He attended commemorations last week for the 80th anniversary of D-Day, the Allied invasion of Nazi-occupied Europe on June 6, 1944.

The princess is expected to join other members of the family on a Buckingham Palace balcony to watch a fly-past of military aircraft. She has not made any public appearances since December.

On Friday, she said in her statement that she is “not out of the woods yet” and officials stress that Saturday’s engagement does not herald a full return to public life.

More than 1,000 soldiers, 250 military musicians and more than 200 horses will take part in the parade.

The equine participants will include Trojan, Tennyson, and Vanquish, three of the five military horses who sparked mayhem in April when they bolted and ran loose through central London.

The horses were performing routine exercises near Buckingham Palace on April 24 when they became spooked by noise from a nearby building site and galloped through the capital’s streets, crashing into vehicles and causing chaos during the morning rush hour.

The army says the other two horses are recovering well and are expected to return to duty.