King feeling better but will be frustrated at visit having to be cancelled

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. That in itself was a sign of how difficult the decision had been to postpone the King's trip.

It is not something the King himself would have wanted.

He was due to undertake four separate engagements in the city. Postponements cause disappointment and disruption but after discussions involving the King, his medical team and his closest advisers, it was the doctors who won the argument. The Birmingham visit will be rescheduled.

It will have been all the more frustrating because the King was "feeling good" last night, according to the Palace. He had dinner with his wife and spent time in his study at Clarence House going through state papers and making phone calls.

It was all a reminder that the King is 76, received his cancer diagnosis in February last year and has been dealing with regular treatment ever since.

There are vulnerabilities that will inevitably show themselves at times.

Managing the King is the challenge all those close to him face, especially his wife.

On several occasions since his diagnosis, Queen Camilla has hinted at her husband's work ethic and how hard it is to get him to slow down - but she will be a very influential voice in his ear.

This time last year the King had scaled his diary right back while he navigated the early stages of his cancer treatment. But those who know him well said this would not last, as getting out and about on public duty was of huge importance to the King and impacted his wellbeing.

The King and Queen's official visit to Australia and Samoa last year was a turning point in terms of the royal diary. It was in some ways a test of his resilience and how he could cope with the rigours of an overseas tour.

• King experiences temporary side effects of cancer treatment

At times he appeared tired but he managed the long journey and several days of engagements while putting his cancer treatment on hold.

When the trip was over, royal sources spoke of its importance to the King on a very personal level. Back in October, one source said: "He's a great believer in mind, body and soul and this combination works very well on a visit like this.

"He feels that sense of duty so strongly which keeps his mind and his soul engaged and then there's a doctor here to keep his body looked after. You've got what makes for a very successful visit in these circumstances."

Those words are revealing, an insight into how public engagements and royal duty were fuelling the King's recovery. But there is a balance to strike.

On Thursday, it was clearly felt that he should step back and have some time to rest this weekend.

The mood at Buckingham Palace is not one of alarm, there is no sense of crisis - but this is obviously unsettling.

Throughout the King's illness, Palace staff have opted for openness and transparency with limits. Last night's statement was made in the spirit of transparency to guard against rumours and speculation.

The details of the King's cancer and the type of treatment he is having remain private, but the fact he is still undergoing treatment is very much public.

The King's health, the Palace says, is still heading in a positive direction.

His schedule will now be reviewed. I am told there may be some "light pruning" but no major changes are expected.

The King has a State Visit to Italy in the diary due to start in the second week of April, though a previously planned meeting with Pope Francis has been cancelled due to the pontiff's ill-health.

As things stand, that trip will go ahead. It is expected that the King will be back in business next week.