Catherine, Princess of Wales has made her first public appearance since being diagnosed with cancer, joining other royals in London for Trooping the Colour, the King’s official birthday parade.

The Princess, also known as Kate, was driven in a state carriage with her three children from Buckingham Palace to Horse Guards Parade to watch the ceremony. She could be seen wearing an Irish Guards regimental broach, a nod towards her role as their honorary colonel.

The family were later seen watching events from a viewing point, while Kate’s husband William, the Prince of Wales, rode on horseback.

King Charles III and Queen Camilla were also taken in a carriage from Buckingham Palace, bringing cheers from the packed crowds as they made their way slowly up The Mall. The King is taking part from a carriage rather than on horseback this year due to his own cancer diagnosis.

People of all ages gathered along the length of the Mall for the event. Some onlookers are wearing Union Jack bucket hats and fascinators, while others are waving flags. The most patriotic have been singing the national anthem.

Kate is expected to join fellow royals on the balcony later. It represents a significant moment in the Princess’s recovery, marking her first public appearance since Christmas Day – weeks before her cancer diagnosis.

Royal fans hold a cardboard cutout of Catherine, Princess of Wales, as they wait on The Mall outside Buckingham Palace. – Henry Nicholls/AFP/Getty Images

Members of the public gather at Buckingham Palace. – Chris Jackson/Getty Images

Kate gave an update on her health on Friday, saying she had made “good progress” in her recovery. But she said she expected her treatment to last for a few more months and was “not out of the woods yet.”

King Charles III is also taking part, despite also undergoing treatment for cancer.

Trooping the Colour is the magnificent military spectacle which sees 1,400 officers and soldiers, together with 400 musicians and 200 horses, process through the streets of London from Buckingham Palace to Horse Guard’s Parade, while crowds line the route.

The event – one of the highlights of the royal calendar – is a tradition marking the official birthday of the British sovereign for more than 260 years. However, Charles’s actual birthday is in November.

Britain’s Kings and Queens have doubled up on their festivities since the 18th century, holding both a public celebration – the official birthday – and a more private event on the real date.

The tradition is believed to have started with the party-mad King George II in 1748. Like Charles III, George was born in November, when British weather is often far from ideal.

Following the pageantry, the parade returns to the palace where the sovereign and members of the family traditionally assemble on the famous balcony to greet cheering crowds of wellwishers below.

Kate’s appearance was a big topic of discussion among onlookers as they chatted and warmed their hands on flasks of tea. “We’re very excited,” Reine Geldenhuys, 41, told CNN.

“We are hoping to walk up to the balcony and see her beautiful face again… We’ve been missing seeing her out in public so we’re here for her mostly,” she added.

This year’s proceedings have been adapted as the 75-year-old Charles continues his treatment for an unspecified form of cancer.

Doctors have been encouraged by his progress, allowing him to resume public-facing duties in April, but each engagement he carries out is reviewed and adapted where appropriate.

For the events on Saturday, he will carry out his review of troops seated in an Ascot landau carriage alongside Queen Camilla.

Three of the British Army’s horses which bolted across in London in April have returned to duty and are expected to take part in this weekend’s birthday parade. The two remaining horses “are enjoying a summer holiday in the Chilterns” and will return to service in due course, according to the army.

This is a developing story and will be updated.

CNN’s James Frater and Rob Picheta contributed reporting.