Buckingham Palace said that after “scheduled and ongoing medical treatment for cancer” on Thursday morning, the King “experienced temporary side effects that required a short period of observation in hospital”.
“His Majesty’s afternoon engagements were therefore postponed,” the statement added.
King Charles latest: Monarch cancels engagements after hospital visit
It said the 76-year-old was now back at Clarence House but “as a precautionary measure, acting on medical advice, tomorrow’s diary programme will also be rescheduled”.
“His Majesty would like to send his apologies to all those who may be inconvenienced or disappointed as a result,” the palace said.
Sky’s royal correspondent Laura Bundock said it was “obviously a concern” but we are being “advised this isn’t a major problem in terms of his ongoing recovery”.
A source also described it as a “most minor bump in a road that is very much heading in the right direction”.
The King revealed in February 2024 that he had been diagnosed with cancer and was beginning a course of treatment.
The form of cancer has not been made public.
In December, sources suggested his treatment would continue into the New Year but said it had been “moving in a positive direction”.
He returned to public duties in April last year despite having weekly treatment.
The King was due to visit Birmingham on Friday. The palace said he was “greatly disappointed” to have to miss it, but it’s hoped the trip can be rescheduled.
The royal couple are also scheduled for a state visit to Italy in just over a week’s time.
Royal commentator Alastair Bruce told Sky News the King was on good form earlier this week.
“Literally two days ago I was standing in front of him when he invested me with some insignia that I received in the New Year’s Honours and I had a fantastic conversation with him,” he said.
“He was standing there for about an hour and a half, handing out honours and awards. He is maintaining as best he can all the challenges and tasks his role requires.”
The King’s programme that day also included knighting Sir Stephen Fry.
