King Charles III spent a short period of time in hospital on Thursday after experiencing temporary side effects during cancer treatment, Buckingham Palace said.

The King returned to Clarence House, where he was said to be continuing to work on state papers and make calls from his study. He has cancelled a tour of Birmingham on Friday, acting on medical advice.

Charles, 76, had planned to travel to the city for a busy schedule of engagements, which included four events.

The palace first announced the King's cancer diagnosis in February 2024.

A Buckingham Palace spokesperson said meetings with three ambassadors on Thursday were also affected.

"Tomorrow, he was due to undertake four public engagements in Birmingham and is greatly disappointed to be missing them on this occasion," the palace's statement added.

"He very much hopes that they can be rescheduled in due course and offers his deepest apologies to all those who had worked so hard to make the planned visit possible."

A palace source described it as a "most minor bump in a road that is very much heading in the right direction".

The palace did not provide further information over what his side effects were.

Queen Camilla attended a reception in Wembley, north London on Thursday and did not join the King during his brief stay at hospital.

After the palace released the news, a spokeswoman for Prime Minister Sir Keir Starmer said he "wishes His Majesty the King all the very best".

The underlying message from the palace is one of reassurance – with the postponement of the visit to Birmingham presented as a brief setback against an otherwise optimistic picture on the King's health.

There was no drama, they went to the London Clinic hospital in central London in a car and not an ambulance, and the late night announcement followed a decision that it was wiser to postpone Friday's visit.

It might also have seemed wiser to get ahead of the news and remain transparent about a minor problem, rather than make it a major event with a last-minute cancellation.

His cancer treatment is ongoing but the King has seemed keen not to be defined by his illness. He seems to thrive on meeting crowds and has shown no signs of slowing down, with a full set of engagements.

In recent weeks, he has been on a trip to Northern Ireland, he launched a playlist of favourite music and attended the Commonwealth Day service, having missed it last year after his cancer diagnosis.

The King has been centre-stage in recent weeks, unexpectedly involved in global diplomacy.

After inviting President Donald Trump for a second state visit to the UK, the King then showed solidarity with Ukraine's President Volodymyr Zelensky after his disastrous meeting with Trump in the White House.

He also welcomed Mark Carney, Canada's new prime minister, whose country has been under pressure from Trump.

None of that suggested that the monarch was running out of energy. The postponement of the state visit to the Vatican, announced earlier this week, had been about the health of Pope Francis rather than the King—with the rest of the visit to Italy expected to go ahead.

While recognising that it is impossible to rule out any further health problems, the message from Buckingham Palace is that the King is expected to be back to normal in terms of his diary next week.

The King's wider state visit to Italy is also set to continue in April with some alterations to the planned programme, the palace said this week.

The palace has never disclosed what type of cancer the King has. He returned to public duties last April after a period of treatment and recuperation.