King Charles was taken to hospital on Thursday, Maech 27, after experiencing side effects from his cancer treatment.
Charles “required a short period of observation” before returning to Clarence House, Buckingham Palace said.
He has cancelled an away day to Birmingham on Friday, March 28, to prioritise his recovery as a precautionary measure.
The King, 76, was said to be on good form at his London home where he is working on state papers and making calls from his study.
A source described it as a “most minor bump in a road that is very much heading in the right direction”.
The King visited the London Clinic on Thursday morning and travelled to and from the hospital by car. He was not joined by the Queen during his brief stay.
Buckingham Palace said in a statement: “Following scheduled and ongoing medical treatment for cancer this morning, the King experienced temporary side effects that required a short period of observation in hospital.
“His Majesty’s afternoon engagements were therefore postponed.
“His Majesty has now returned to Clarence House and 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.”
Charles was diagnosed with an undisclosed form of cancer in February 2024 and returned to public-facing duties in April despite still undergoing weekly treatment.
He has had a busy run of engagements this month, including a reception for media on Wednesday evening after a visit to a soil exhibition in the day, and is due to make a historic state visit to Italy in 10 days’ time.
It is understood the overseas tour with the Queen from April 7-10, which will see Charles become the first British sovereign to address both houses of the Italian parliament, is expected to go ahead as planned.
Last week, the King made a whirlwind three-day visit to Northern Ireland with Camilla, and earlier in March hosted high-profile audiences with key political figures including Ukrainian president Volodymyr Zelensky, outgoing Canadian prime minister Justin Trudeau and new Canadian PM Mark Carney.
Charles, who is known for being a workaholic, is said to have thrived on carrying out public and state duties in recent months, seeing them as being of great benefit to his overall wellbeing.
His long-haul visit to Australia and Samoa last autumn was described at the time as the ‘perfect tonic’ for the monarch.
Since his diagnosis last year, the King’s diary of engagements is understood to have been developed in full consultation with his medical team at all stages to protect and prioritise his recovery.
Sources stressed the hospital visit was not a major development and no further updates are expected on the King’s health, with any minor alterations to his diary that may be required next week being announced in due course.
The King was due to meet ambassadors in audiences at Buckingham Palace on Thursday afternoon but these were postponed due to his stay in hospital.
He also had a busy day planned in Birmingham on Friday, with four engagements back to back.
The London Clinic was the same hospital where he was treated for an enlarged prostate in January last year, and also where the Princess of Wales had abdominal surgery the same month.
The specifics of the King’s side effects have not been disclosed but they are understood to be temporary and not uncommon with many medical treatments.
The announcement from the Palace is understood to have been made late on Thursday because time was required for the King to consult his staff and medical team on his return to Clarence House.
It was decided on balance that it was wiser to cancel the visit to Birmingham as a precautionary measure.
A Buckingham Palace spokesperson said: “His Majesty was due to receive credentials from the ambassadors of three different nations this afternoon.
“Tomorrow, he was due to undertake four public engagements in Birmingham, and is greatly disappointed to be missing them on this occasion.
“He very much hopes that they can rescheduled in due course and offers his deepest apologies to all those who had worked so hard to make the planned visit possible.”
