King Charles to attend Easter Sunday service since revealing a cancer diagnosis.

Britain’s head of state, King Charles III, will attend an Easter Sunday church service, Buckingham Palace announced Tuesday, in his most high-profile engagement since revealing a cancer diagnosis.

Charles and his wife, Queen Camilla, will attend the Easter Mattins Service at St George’s Chapel at Windsor Castle — a long-standing annual tradition of Britain’s royal family.

The announcement comes after the 75-year-old king’s daughter-in-law Catherine, Princess of Wales, last week said that she was also receiving treatment for cancer.

That leaves the monarchy in an unprecedented crisis in modern times, with two of its most senior members simultaneously fighting serious illness.

Catherine, 42, is married to Charles’s eldest son and heir, Prince William, making her a future queen.

Charles was just 17 months into his reign when the palace announced in early February that he had cancer and would be pausing all public-facing engagements as he commenced treatment.

He had been admitted for surgery for a benign prostate condition in January but was subsequently diagnosed with an unrelated cancer.

He has been continuing with behind-the-scenes work and holding some in-person meetings and increasingly attending official events.

On Tuesday, he was photographed receiving community and faith leaders at Buckingham Palace in central London.

Last week, photos showed him meeting diplomats at the palace, as well as veterans of the Korean War, at two separate engagements.

Charles said in a statement earlier this month that he would continue to serve “to the best of my ability”, and he had been “deeply touched” by people’s wishes for his health.

He praised Kate, as she is widely known, for her bravery last week by revealing in a video message that she was undergoing chemotherapy.

She was last seen at a public engagement on December 25, then underwent abdominal surgery in January, after which cancer was found.

Her Kensington Palace office said at the time that she was not expected to be ready to return to public duties until after Easter.