The King has greeted well-wishers in an impromptu walkabout after an Easter church service in Windsor, his first appearance at a public royal event since his cancer diagnosis was announced in February.

A smiling monarch, 75, accompanied by Queen Camilla, shook hands with scores of people gathered outside St George’s Chapel, the resting place of his late mother Queen Elizabeth.

While the King attended church on Sunday, his son Prince William and his family did not.

William’s wife Kate said earlier this month she was have preventative chemotherapy after cancer was discovered following abdominal surgery in January.

The King and Queen at the Easter Mattins Service at St George’s Chapel at Windsor Castle in Berkshire. Photo: AAP

One man told Charles on Sunday: “Happy Easter Your Majesty. Keep going strong, keep going strong, never give in.”

Another member of the public told the King: “We’re all rooting for you, we’ve all got your back.”

The King shook hands and spoke with those who had gathered at Windsor and told them: “You’re very brave to stand out here in the cold.”

Tweet from @KateMansey

The King had postponed all previous public engagements since Buckingham Palace announced he was to undergo treatment for an unspecified form of cancer.

The illness was found in tests after he had a corrective procedure for an enlarged prostate in January.

The King, wearing a dark overcoat, and Queen waved to onlookers when they arrived at the chapel by car from their residence at Windsor Castle.

The King’s sister, the Princess Royal, and brother, the Duke of Edinburgh, accompanied by their spouses, also attended. The Duke of York, who was removed from royal duties in 2022 due to his friendship with the late sex offender Jeffrey Epstein, was also there with ex-wife Sarah Ferguson.

Princess Anne at St George’s Chapel on Easter Sunday. Photo: AAP

The King has kept up with the bulk of his non-public state duties such as greeting foreign officials and holding regular meetings with British Prime Minister Rishi Sunak.

Last week the King did not attend an annual Maundy Thursday service but issued an audio message that aired at the event, in which he expressed his sorrow at not being there and wished the public a happy Easter.

-AAP with PA