Buckingham Palace announced on Monday that, during recent prostate surgery, doctors noted that King Charles III had a form of cancer.
During his hospital procedure for benign prostate enlargement, "a separate issue of concern was noted. Subsequent diagnostic test have identified a form of cancer," a statement from the Palace said.
What did Buckingham Palace say?
"His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by his doctors to postpone public-facing duties," it added. "Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual."
After thanking his medical team for their "swift intervention," the Palace said that the king "remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible."
The decision to share, or at least partially share, Charles' diagnosis was made to "prevent speculation" and to "assist public understanding for all those … affected by cancer," Buckingham Palace wrote.
Charles underwent prostate surgery on Friday, January 26 before being discharged on Monday, January 29.
Political leaders rush to convey well wishes
The speaker of Britain's lower house of parliament, Lindsay Hoyle, told the House of Commons of the news shortly after the announcement. "We all wish to send him our very best wishes for successful treatment and a speedy recovery following tonight’s news," Hoyle told the chamber.
British Prime Minister Rishi Sunak was also quick to comment online.
"Wishing His Majesty a full and speedy recovery. I have no doubt he’ll be back to full strength in no time and I know the whole country will be wishing him well," Sunak wrote.
The leader of the opposition Labour Party, Keir Starmer, said: "On behalf of the Labour Party, I wish His Majesty all the very best for his recovery. We look forward to seeing him back to swift full health."
"The Liberal Democrats join the rest of the nation in wishing a full and quick recovery to His Majesty," Liberal Democrats leader Ed Davey also said.
Meanwhile a State Department spokesman in the US told reporters in Washington that "our thoughts are with the king ... and his family," describing the development as "incredibly sad news."
Long wait for throne ended in 2022
Charles, 75, took the throne around 16 months ago following the death of his mother, Queen Elizabeth II, in September 2022.
His coronation took place last June. Charles has often stated his desire to modernize the monarchy and is a well known advocate on environmental matters and climate change.
He celebrated his 75th birthday on November 14 last year by launching the Coronation Food Project aimed at tackling food poverty and reducing waste. He launched the initiative via an interview with magazine The Big Issue, which is sold to raise money for the homeless in Britain and which he had supported since its foundation in the 1990s.
Harry planning visit, Princess of Wales also sidelined after surgery
According to the UK Press Association news agency, King Charles' younger son Harry had spoken to his father and was planning to travel to the UK in the coming days. He now lives in the US with his wife having stepped back from regular royal duties.
Meanwhile, the Princess of Wales, Katherine, is continuing her recovery from abdominal surgery in January. This has also sidelined her from royal duties.
Her husband, Prince William, is scheduled to return to his official duties on Wednesday for the first time since her two-week spell in hospital. The Royal Family had not said what condition Kate was receiving treatment for, but had specified at the time that it was not cancer.
This had meant that for a time Charles' wife, Queen Camilla, was the most prominent royal member still available for public appointments.