A number of plans the King had today had to be canceled because of side effects from his cancer treatment.
Charles, who is 76 years old, had a “scheduled” visit today as part of his treatment.
But he had “temporary side effects” that meant he had to stay in the hospital for a short time to be watched.
Tonight, the King was back at Clarence House “working away as usual.” Sources said it was just a “most minor bump in the road that’s very much heading in the right direction.”
They said that he had to “regretfully” cancel plans to go to Birmingham tomorrow in order to “protect and prioritize [his] continued very positive recovery.”
Sources said there was “no drama” and that the “brief” trip to the hospital was “related to [his] treatment plan.”

But it’s a sobering reminder that the King is still getting treatment for cancer more than a year after saying he had been diagnosed with a type of cancer that wasn’t made public. He also has a full schedule of public events.
A source added: “As many can vouch, such things are not unexpected with these kind of conditions.”
Buckingham Palace said tonight: “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.”
Buckingham Palace has never said what kind of cancer the King has or how he is being treated. They only said that it has nothing to do with the surgery they did on his prostate in January of last year, which is how they found the disease.
That being said, the Mail has said that it was caught very early on. It is known that he is still getting treatment and that his recovery is moving “in a very positive direction.”
According to sources, the King has been able to do all of his public and official tasks, and that will not change.
He was last seen in public on Wednesday, when he had two long events: first, he went to an exhibition about soil and met farmers; then, he hosted a big party at Buckingham Palace for 400 people from the regional media.
It took him more than an hour to meet and greet all of his guests. Queen Camilla recently talked about how upset she is that her husband won’t slow down.
To protect his medical privacy, he has tried to be as open as possible about his diagnosis. He wanted to share the latest news in a “spirit of openness and transparency.”
It hasn’t been made clear what the side effects are yet, but reports say they are
not unusual with many medical methods.
Last night, the King was said to be in “good form” at home. He is still working on State papers and making calls from his study.
He was taken care of at The London Clinic, which has helped him before, and he normally drives to and from the hospital.
The Queen did not go with the King to the hospital yesterday for his short stay.
A spokesman said of the cancelled engagements, “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 be rescheduled in due course and offers his deepest apologies to all those who had worked so hard to make the planned visit possible.”
No big changes are expected to his schedule, but it may be decided to lighten some parts of the full plan based on the advice of his medical team and in time for the royal couple’s State visit to Italy in a little over a week.
It is known that the visit that starts on April 7 will happen.
Charles hasn’t taken much time off in the past year, except for the first few weeks after being diagnosed. He quickly returned to his public tasks, first in private and then in public.
In the fall of 2016, he even went on a tough two-week tour of Australia and Samoa.
Sources say that the King’s general health has improved a great deal since taking on public and State duties. Charles is “deeply grateful” for all the support, encouragement, and kind words he has received from the many thousands of people he has met while doing these things.
According to Buckingham Palace, there won’t be any more updates because what happened is “not a major development.” However, they will let everyone know in due time if there are any minor changes that need to be made to next week’s schedule.