Britain’s King Charles III attended an Easter church service on Sunday, in his most high-profile public appearance since revealing a cancer diagnosis earlier this year.

Charles and his wife, Queen Camilla, arrived by car for the hour-long late morning service at St. George’s Chapel within the grounds of Windsor Castle, west of London.

The 75-year-old, dressed in a suit and light blue tie, smiled and waved to crowds — who had queued up for hours for a glimpse of the ailing monarch — before he entered the chapel.

Leaving the service, Charles and Camilla greeted some of the well-wishers lined up outside, shaking hands and briefly chatting to some in the crowds.

Attending the annual religious ceremony is a long-standing annual tradition for the royals, with other family members in attendance.

But heir-to-the-throne Prince William and his wife Catherine were notable absentees this year, as the 42-year-old Princess of Wales receives treatment following her own cancer diagnosis, which was revealed just last week.

The situation represents an unprecedented crisis in modern times for the monarchy, as two of its most senior members simultaneously fight serious illness.

Charles was just 17 months into his long-awaited reign when Buckingham 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. The type of cancer has not been disclosed.

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