King Charles III's cancer has been “caught early”, UK Prime Minister Rishi Sunak revealed on Tuesday, as he wished him a full recovery.
Buckingham Palace on Monday announced the monarch has been diagnosed with cancer, but declined to say which type.
The palace said the king, who acceded to the throne 17 months ago, does not have prostate cancer, despite having treatment for an enlarged prostate just over a week ago.
The king, 75, will suspend public engagements but continue with state business while he undergoes a schedule of regular treatment.
He was discharged from hospital last week, three days after undergoing scheduled surgery for an enlarged prostate.
He returned to London from Sandringham on Monday and has already begun his treatment as an outpatient under the supervision of his specialist team of doctors.
The Prime Minister said he was left “shocked and sad” when he was told about the king's cancer diagnosis.
Mr Sunak said in a radio interview on Tuesday: “All our thoughts are with him and his family.
“Thankfully, this has been caught early.”
He said everyone will be hoping the king “gets the treatment that he needs and makes a full recovery”.
Prince Harry was expected to arrive in the UK shortly to be with his father, despite their troubled relationship.
The duke's black Range Rover was pictured arriving at a private terminal at Los Angeles International Airport on Monday to board a flight.
The Prince of Wales, Queen Consort Camilla and other working royals will step up their royal duties while the king undergoes treatment.
Buckingham Palace has confirmed a number of the king’s forthcoming public engagements will have to be rearranged or postponed.
In the event a monarch cannot undertake their duties as sovereign on a temporary basis due to illness, two or more Counsellors of State can be appointed by Letters Patent to act in their place.
The palace suggested the king will continue with some of his duties, but how much he can do will depend on the progress of his treatment and the orders of his doctors.
Other members of the royal family are expected to continue with a full programme of public engagements and may undertake some additional duties on behalf the king if they are required to do so.
Usually the duty would fall to Prince William in the first instance, who has recently returned to royal duties after the Princess of Wales underwent major abdominal surgery last month.
Cancer charities and health professionals praised the king for being open about his diagnosis.
Professor Pat Price, founder of the Catch Up With Cancer campaign, said the outpouring of well wishes “reflects the collective concern we all share”.
A look at King Charles's health over the years
The king has generally enjoyed good health, although he has been injured during sporting pursuits.
Previous health issues have included contracting coronavirus at the start of the pandemic and being knocked unconscious after being thrown from his horse while playing polo. He also narrowly escaped an avalanche that killed a close friend.
Concern has been expressed over the years at his “sausage fingers” amid fears they might be due to fluid build-up or other conditions.
But King Charles had been aware of his puffy fingers for decades.
“He really does look surprisingly appetising and has sausage fingers just like mine,” he wrote to a friend after the birth of his first son, Prince William, in 1982.
In March 2020, the monarch, who was 71 at the time, caught Covid-19 before vaccinations were available, but had mild symptoms and isolated at Birkhall, Aberdeenshire, away from the Duchess of Cornwall at the time, who tested negative. He carried on working at his desk while recovering.
He lost his sense of taste and smell for a time and later spoke of the “strange, frustrating and often distressing” experience of being without friends and relatives during lockdown.
He caught Covid for a second time in February 2022 but had, by then, received three vaccine shots.
The king has kept active with walking in the hills and gardening but did suffer from back pain, attributed to falls from horses over the years while playing polo.
A devotee of organic food, he launched his food brand, Duchy Originals, in 1990, which is now run as Waitrose Duchy Organic.
In March 2019, as the king and queen consort began an official tour of the Caribbean, they were photographed by the paparazzi relaxing on a beach in Barbados in their swimming costumes.
King Charles won praise for his figure and his on-trend, 12-year-old floral trunks.
In 2008 he had a non-cancerous growth removed from the bridge of his nose in a minor, routine procedure, and in 2003 had a hernia operation at the private King Edward VII’s Hospital in London, the hospital favoured by the royal family.
He joked “hernia today, gone tomorrow” to the waiting media after being discharged the next day.
Back pain attributed to falling from horses while playing polo
In 2003, during an engagement at a Sikh temple in Southall, west London, he told the congregation that he would need a little of their expert care as he sat on the hard floor.
“I don’t think I have ever needed an osteopath so much as I have today,” he joked.
King Charles has been an advocate of alternative and complementary medicine, including homoeopathy.
He was patron of the regulatory body the General Osteopathic Council.
He urged health ministers to adopt a more holistic approach to tackling health problems.
King notches up injuries from 40 years of playing polo
King Charles retired after more than 40 years of playing polo in 2005, having notched up an array of injuries.
In 1980 he was thrown and kicked by his pony during a polo match at Windsor and needed six stitches.
A two-inch crescent scar on his left cheek bore witness to the incident.
On another occasion he was hit in the throat, causing him to lose his voice for 10 days.
He resisted pressure to give up polo after he collapsed in 1980 at the end of a game in Florida and had to be put on a saline drip.
In 1990 he broke his right arm in a fall during a polo match, among other injuries.
He also broke a rib when he fell from his horse in a hunting accident in 1998.
He insisted on trekking in the Himalayas a few weeks afterwards during an official visit to Nepal and Bhutan.
Three months later in October 1998, he was back in hospital undergoing laser keyhole surgery on his right knee cartilage due to wear and tear from years of sport and exercise.
In June 2001, he fractured a small bone in his shoulder after falling off his horse during a fox hunt.
A few months later in August 2001, he was knocked unconscious and taken to hospital when his horse threw him during a polo match.
He was carried off on a stretcher and taken by ambulance to hospital as a precautionary measure.
King Charles has also strained tendons in his wrist while salmon fishing in Scotland and injured himself gardening.
While tending to his gardens he once accidentally hit his thumb with a mallet and broke his finger, almost severing the tip.
King Charles has said he was rushed to Great Ormond Street Hospital, aged 13, to stop his appendix from “exploding”.
He declared on a later visit: “I got here just in time before the thing exploded and was happily operated on and looked after by the nurses.”