King Charles will attend the Easter Sunday service at St. George's Chapel in Windsor, in what will be his first public appearance at a traditional royal event since his cancer diagnosis was revealed in February.
Buckingham Palace said on Tuesday that Charles, 75, and his wife Queen Camilla will attend church on March 31, typically an occasion for a gathering of senior royals.
The announcement comes days after Kate, Princess of Wales, and the king's daughter in law, said she had also had a cancer diagnosis and was undergoing preventative chemotherapy.
The Easter service this year will be smaller in scale due to the king's health, Buckingham Palace said.
Kate and heir to the throne Prince William will not attend, their office had already announced.
Since his diagnosis, Charles has cut back his public appearances as he receives treatment. He missed Commonwealth Day celebrations earlier in March, an absence from what is a significant occasion in the British monarchy's annual calendar.
But he appears to be gradually stepping up his public engagements.
He met faith leaders at Buckingham Palace earlier on Tuesday, who were part of a programme aimed at fostering harmony and sharing experiences of leadership at a time of heightened geopolitical tensions.
The confirmation that he will attend church on Sunday follows news that Charles was finding the pace of his recovery frustrating, according to his nephew Peter Phillips, a rare insight into how he was faring.