Britain's Catherine, Princess of Wales waves as she arrives to attend the men's singles final tennis match on the fourteenth day of the 2024 Wimbledon Championships at The All England Lawn Tennis and Croquet Club in Wimbledon, southwest London, on July 14, 2024. Henry Nicholls, AFP/File

LONDON -- Britain's Catherine, Princess of Wales, took a significant step in her recovery from cancer on Saturday as she attended her first major royal occasion since ending chemotherapy.

Kate, as she is widely known, smiled and clapped alongside her husband Prince William at the Festival of Remembrance commemorative concert at the Royal Albert Hall in London.

The musical event is one of the most important dates in the royal calendar, along with Sunday's more solemn ceremony at the Cenotaph war memorial, both of which honor Britain's war dead.

Catherine and William were joined in the royal box by head of state King Charles III, who is still undergoing treatment for his own cancer diagnosis.

READ: Catherine, Princess of Wales says she has completed chemotherapy

READ: Catherine, Princess of Wales makes tentative return to work

Buckingham Palace in February announced that Charles, 75, had been diagnosed with an undisclosed cancer and would withdraw from public life to undergo treatment.

The following month Kate, 42, revealed that she too had been diagnosed with cancer and was undergoing chemotherapy.

Both have since made limited returns to public duties, with Charles recently pausing his treatment while on tour in Australia and Samoa.

Catherine said in September that she had completed her chemotherapy and was looking forward to undertaking more engagements "when I can".

Last month, she and heir to the throne William visited Southport in northwest England to meet people affected by a knife attack in July that killed three young girls.

Catherine is among senior royals also due at Sunday's wreath-laying at the Cenotaph near parliament alongside political leaders, current and former members of the armed forces, including war veterans.

It will be the first time she has carried out two consecutive days of public official engagements since the start of the year.

William said this week that the past year had been "brutal" and probably the "hardest" of his life because of the twin diagnoses.

"Honestly, it's been dreadful," he told reporters on Thursday at the end of a four-day visit to South Africa for his Earthshot prize initiative.

"So, trying to get through everything else and keep everything on track has been really difficult."

Queen Camilla, Charles's wife, missed Saturday's concert, and was to also skip the Sunday service as she continues to recover from a chest infection, the palace said.

She "hopes to return to public duties early next week," a palace spokesperson said.

© Agence France-Presse