He had canceled almost all public engagements.
King Charles III, who is currently being treated for cancer, will attend the traditional Easter mass in Windsor on Sunday, Buckingham Palace announced in a statement on Tuesday.
He will travel to St George's Chapel in Windsor in the morning with Queen Camilla and other members of the royal family.
The heir to the throne William, and his wife Kate, who revealed on Friday that she also has cancer, will however be absent, taking some rest away from media attention with their children.
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Buckingham Palace announced in early February that the king was suffering from cancer, discovered during a prostate operation a few days earlier, and had begun treatment.
Charles III has since canceled all official public engagements, but continues to carry out certain official functions or small meetings, such as his meetings with the Prime Minister.
On Tuesday, he received representatives of different religions at Buckingham Palace.
Return to public functions after the Easter holidays?
Last Friday, the Princess of Wales Kate announced in turn that she had cancer, without specifying its nature, and that she had started chemotherapy.
His cancer was discovered after a major abdominal operation which took place in mid-January.
The king said he was "proud" of her courage, after weeks of speculation in the media and on social media sparked by Kate's lack of public appearance since Christmas.
According to the British agency PA, the Prince of Wales is expected to return to his public duties after the Easter holidays and the return to school of the couple's children, George, Charlotte and Louis.