King Charles III has been admitted to hospital after suffering "temporary side effects" during his "scheduled and ongoing medical treatment for cancer", Buckingham Palace has said.
The 76-year-old "required a short period of observation in hospital" on Thursday morning, the palace said.
His afternoon engagements were postponed "as a precautionary measure" and "acting on medical advice".
LONDON, ENGLAND - MARCH 26: King Charles III waves during a visit to the 'Soil: The world at our feet' exhibition at Somerset House on March 26, 2025 in London, England. King Charles III is Patron of The Royal Countryside Fund. The visit coincides with the 25th anniversary of Somerset House. (Photo by Chris Jackson/Getty Images)
King Charles pictured in London on Wednesday. (Getty)
King Charles has since returned to Clarence House, his residence in London.
The full statement from the palace, sent on Friday morning in Australia, reads: " 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."
BELFAST, NORTHERN IRELAND - MARCH 19: King Charles III and Queen Camilla are serenaded with a sea shanty as they visit Commercial Court during an official visit to Northern Ireland on March 19, 2025 in Belfast, Northern Ireland. (Photo by Charles McQuillan/Getty Images)
The King and Queen were in Northern Ireland last week. (Getty)
Buckingham Palace has not revealed the nature of the King's treatment.
In April last year the monarch returned to public-facing duties after an extended period away on the advice of his medical team.
This is a breaking story, more to come.