Charles, who is undergoing treatment for cancer, is head of the Church of England and the service is an important fixture of the royal calendar.
The King is to make his most significant public appearance since he was diagnosed with cancer when he attends church on Easter Sunday.
Charles, 75, will join the Queen and other members of the royal family at the annual Easter Mattins Service at St George’s Chapel at Windsor Castle this weekend.
The Prince and Princess of Wales and their children Prince George, Princess Charlotte and Prince Louis will not be present.
The family are spending the Easter holidays together as they adjust to Kate’s cancer diagnosis.
Confirmation of the King’s appearance comes just four days after the princess released an emotional video message revealing she has started a course of preventative chemotherapy.
Post-operative tests following her major abdominal surgery showed she had cancer.
Charles’s Easter Sunday engagement will be seen as the King making a move to reassure the public following the shock news.
The King is still undergoing treatment for cancer himself, but has been carrying out low-key official duties behind palace walls.
Although the Easter service is within the grounds of the castle, the King and Queen will be seen arriving, and are often watched by staff living at Windsor, who usually gather on a grassy bank nearby or watch from their doorsteps.
