LONDON — King Charles III has arrived at the Easter Sunday service at the chapel in Windsor Castle — his first major event since he was diagnosed with cancer in February. 

Charles, 75, was accompanied by Queen Camilla and other members of the royal family at the Gothic-style St. George’s Chapel for the traditional annual engagement.

The king’s public appearance will provide a timely boost to the royal family, which has been beset by illness and media speculation. But the absence of Prince William and Kate, the Princess of Wales, after the revelation of her own cancer diagnosis offered a reminder that the royal ranks remain depleted.

Charles is undergoing regular treatment and has stepped back from public engagements on medical advice, though he has continued to carry out many of his duties behind closed doors.

Officials have not disclosed what form or stage of cancer he has.

On Thursday, he delivered his first public remarks since Kate announced she had become the second senior royal to be diagnosed with cancer, stressing the importance of friendship, “especially in a time of need.”

The pre-recorded audio message was heard at a traditional Maundy Thursday service at Worcester Cathedral, in the city of the same name around 130 miles northwest of London.

Charles said Jesus set an “example of how we should serve and care for each other,” and how “we need and benefit greatly from those who extend the hand of friendship to us, especially in a time of need.”

Although he did not address his daughter-in-law’s health directly or name her in his brief personal message, some royal watchers interpreted his words in the context of the ongoing family health crisis.

The king’s public relations team also released a new picture of the smiling monarch sitting at a desk in Buckingham Palace’s 18th Century Room, apparently recording his address into a microphone.

Charles has spoken of how touched he is by the outpouring of messages and cards from well-wishers from across the United Kingdom and beyond as he undergoes treatment for cancer.

In a statement after Kate revealed her diagnosis last Friday, he said he had become closer to his daughter-in-law through their shared hospital stays. The king was “so proud of Catherine for her courage in speaking as she did,” it added.

Kate said in a video statement that she was undergoing “a course of preventative chemotherapy” on the advice of her medical team.

She did not specify what type of cancer she has or at what stage it was found, and Kensington Palace, the couple’s royal household, has not said why the operation was necessary.

Inside palace doors, the shock of her diagnosis “was immense,” NBC News royal contributor Katie Nicholl told “TODAY” on Friday.

“Kate’s cancer diagnosis was kept was within a very, very, very tight group of people,” Nicholl said. “It was William, it was the king, it was Camilla and of course Kate’s family. But I do know that while Queen Camilla knew, she didn’t even tell her own children.”

William, Kate and their children — George, 10, Charlotte, 8, and Louis, 5 — attended the Easter Sunday service last year, but Kate asked for privacy in her personal video message announcing her diagnosis.