Charles took part in 372 public engagements last year, even after stepping aside for almost three months because of cancer treatment, according to data compiled by The Times of London newspaper. That made him the second-busiest royal behind his sister, Princes Anne, who had 474 engagements.

King Charles was hospitalized briefly, more than a year after his cancer diagnosis, due to what Buckingham Palace called "temporary side effects" of his treatment.

The announcement from Buckingham Palace that King Charles had been in hospital after experiencing side effects from his cancer treatment came hours before he was due to visit Birmingham on Friday. The official statement was released at 21:00 GMT on Thursday.

King Charles III waved to well-wishers in central London on Friday as he headed for his country estate in western England a day after he was briefly hospitalized because of side effects from a scheduled cancer treatment.

Princess Anne is also a supportive sister. After news broke that King Charles had been hospitalized for side effects from his cancer treatments, Princess Anne stopped by to check on her older brother.

King Charles has been seen in public for the first time since he went to hospital after experiencing temporary side effects from his cancer treatment. He cancelled a trip to Birmingham on Friday on medical advice after spending a short period of time in hospital on Thursday,

The news from Buckingham palace was shocking. Over a year after King Charles had announced that he had been diagnosed with cancer, the Palace issued a statement saying the King had experienced side effects from his treatment that were sufficiently severe to warrant observation in hospital.

King Charles' appointments were canceled after his "short period of observation in hospital," Buckingham Palace said.