It comes just days after the King was released from the London Clinic where he had been undergoing ‘routine treatment’ for an enlarged prostate.
It is not the first time the King, 75, has taken a blow to his health and has often joked about his physical decline.
He previously told a crowd in Brisbane in 2018: ‘I don’t know about you but now bits of me keep falling off at regular intervals.’
Here, MailOnline lists some of Charles’ known health issues he has experienced over the years.
King Charles III has been diagnosed with cancer, the Palace confirmed today in a shock announcement
It is not connected with his recent surgery and is not prostate cancer , but medics spotted it when he underwent his medical procedure for an enlarged prostate.
Chronic neck and back pain
Prince Harry revealed in his bombshell memoir Spare that his father suffered from chronic neck and back pain.
The Duke of Sussex, who will fly to London in the coming days to see his father, wrote that Charles has battled ‘constant neck and back pain’ for which he partly credited to his old polo injuries.
Chronic back pain — described as aching, hot, burning, shooting or stabbing agony — affects roughly one in 13 adults, data suggests.
And eight in 10 people will suffer back pain at some point in their life.
It can be caused by an array of factors, including a pulled muscle, a slipped disc — when soft tissue between the bones in the spine bulges out — and sciatica, which is a trapped nerve.
Charles himself slipped a disc in the early 1990s, which saw him miss Royal Ascot in 1991. Two years later, he aggravated the injury when he fell off a horse at Windsor.
He agreed to only play for charity after warnings from his doctor that his condition could worsen if he kept playing competitively.
His trademark walk — with his fingers interlinked behind his back — is thought to be a therapeutic trick to help ease his back pain. By opening his chest and pulling his shoulders back, the technique stops him from slumping when he walks.
The Duke of Sussex wrote in his sensational memoir that Charles has battled ‘constant neck and back pain’ for which he partly credited to his old polo injuries
King Charles wincing in pain after a game of polo at Hurtwood Park in Surrey in 2004
King Charles’s so-called ‘sausage fingers’ have drawn much attention from royal watchers over the years.
But Charles has been aware of his puffy fingers, medically known as dactylitis, for decades.
Writing to a friend after the birth of William in 1982, Charles joked: ‘He really does look surprisingly appetising and has sausage fingers just like mine.’
His late mother, Queen Elizabeth II, famously noted that her firstborn had large digits when he was a mere baby.
And his large hands were a feature the Queen described in a letter to her music teacher after Charles had been born.
She wrote: ‘The baby is very sweet and we are enormously proud of him. He has an interesting pair of hands for a baby.
‘They are rather large, but with fine long fingers quite unlike mine and certainly unlike his father’s.
‘It will be interesting to see what they become.’
However, the King has never confirmed what the actual cause of his predicament is.
GP Chun Tang, medical director at Pall Mall Medical in Manchester, said: ‘There are numerous reasons a person may suffer with ‘sausage’ fingers.
‘Often puffy fingers are a symptom of water retention which can be caused by numerous health conditions.
‘This condition arises due to inflammation and can be a result of arthritis, multiple bacterial infections or even TB.
‘Other possibilities include high salt levels, allergic reactions, medicinal side effects, injury and autoimmune diseases.’
King Charles’s so-called ‘sausage fingers’ have drawn much attention from royal watchers over the years
A doctor explained what may be the root cause behind King Charles’ swollen fingers, for which the official medical term is dactylitis
King Charles had a non-cancerous growth removed from the bridge of his nose in a minor procedure in 2008.
The Royal was seen with a small, hexagonal plaster on the right side of his nose following the surgery at his London residence, Clarence House, in May that year.
Clarence House would not discuss details of what they described as a ‘minor surgical procedure’, stating only that it was ‘a routine and minor matter’.
Other members of the royal family also have a history of receiving treatment for growths on their faces.
Charles’ father, the Duke of Edinburgh, underwent a minor procedure in 1996 to erase a small benign growth on his nose.
In January 2003 the Queen also had minor – non-cancerous – growths removed from her face by surgeons.
Charles broke his right arm after falling from his horse during a polo match at Cirencester in 1990.
The accident, during the second chukka, was described by a spokesman as a ‘nasty break above the right elbow’.
Charles, then 41, was galloping to cut off an opponent when his pony swerved to the right as he leaned over to take a backhand shot. He lost his balance and tumbled between the two animals, one of which kicked him in the arm.
Author Jilly Cooper, who was among the spectators, said at the time: ‘It looked for a moment as though he might have bought it [been killed]. The ground went completely quiet.’
The Royal spent three nights in hospital, dismissing his injury as a ‘silly thing to do’.
But the wound failed to heal properly and after three months of pain – and a warning that, untreated, it could leave him so badly crippled he would be unable to salute – he had an operation to fix it.
Bone was taken from his hip and packed around the break and a metal plate was secured with screws. He was discharged from hospital a week later and was back on the field within the year.
King Charles had a non-cancerous growth removed from his face in a minor procedure in 2008
Charles broke his right arm after falling from his horse during a match at Cirencester in 1990
Charles fell awkwardly from his horse during a hunt in 2001 and broke his acromion, a small bone on the edge of the shoulder blade
Years later, during a fox hunt in Derbyshire in January 2001, Charles’s horse took an ‘unexpected jump’ and flung him to the ground.
He fell awkwardly and it was thought he had dislocated his shoulder.
Royal protection officers, who were riding with Charles in the Meynell Hunt, drove him to a nearby hospital – where an X-ray revealed he had, in fact, broken his acromion, a small bone on the edge of the shoulder blade.
‘He’s fine,’ his spokesman insisted at the time. ‘It was a minor injury and it’s just inconvenient, that’s all. He’s not in any pain.’
Charles had to wear a sling for several days while the fracture healed.
His first polo accident occurred in 1980, when he was thrown and kicked by his pony during a match at Windsor. Charles needed six stitches, leaving a two-inch crescent-shaped scar on his left cheek.
All those years of wear and tear took their toll on Charles’s legs, and in 1992 he had an operation to repair torn cartilage in his left knee.
Six years later, in 1998, he needed keyhole laser surgery to repair damaged cartilage in his right knee.
He had the same surgery on his left knee several years previously — the result of decades of trekking, skiing, polo-playing and generally refusing to sit still.
The operation left him walking with a stick — but two days later, against his aides’ advice, he ditched it and resumed work with a full day of royal engagements.
There were some curious stares in November 2001 when Charles reported for royal duties sporting a rather alarming bandage over his left eye.
It transpired the Prince had been sawing a branch off a tree at Highgrove, his Gloucestershire estate, when he managed to get sawdust in his eye.
The dust scratched his cornea and temporarily affected his vision. After treatment from a local doctor, he was transferred to a specialist and prescribed a day’s rest.
A Palace spokesman said his eye was ‘still sore’ several days later, when Charles proudly displayed his patch at a meeting of business leaders.
In January 1998, Charles was galloping across the Welsh countryside with the Wynnstay Hunt when he fell from his horse and broke a rib.
Despite his discomfort, the injury-prone Royal insisted on going trekking in the Himalayas a few weeks later, as part of an official visit to Nepal and Bhutan.
In 1998 Charles needed keyhole laser surgery to repair damaged cartilage in his right knee
In November 2001, Charles sawed a branch off a tree at Highgrove, his Gloucestershire estate, and managed to get sawdust in his eye
Fall from a horse
In August 2001, Charles was thrown off a horse in a goalmouth skirmish during a charity match at Cirencester Park in Gloucestershire.
The head-first fall knocked him unconscious and he was in danger of swallowing his tongue until a paramedic rushed onto the pitch.
Charles was carried off on a stretcher and some of the horrified crowd, which included supermodel Claudia Schiffer, later admitted they thought he was dead.
He was taken first to Cirencester Memorial Hospital and then to Cheltenham General. Although bruised and shaken, the then 52-year-old didn’t break a single bone.
William and Harry, 19 and 17 at the time, were also playing and carried on after their father’s injury. Highgrove went on to win against local rivals Edgeworth.
In 1981, a stray polo ball — presumably hit by an over-zealous opponent — flew directly into Charles’s throat during a match.
The incident left him winded and clutching his larynx.
Although he suffered no permanent damage, Charles lost his voice for ten days — leaving him uncharacteristically mute.
Charles had an op on a hernia in March 2003, which was reportedly caused by a gardening injury from working in the grounds at Highgrove.
The condition, caused by a loop of the bowel protruding through an abdominal muscle, left Charles in considerable pain — and the subsequent operation meant he had to cancel his annual skiing holiday in Klosters, Switzerland.
At the time, he joked ‘hernia today, gone tomorrow’ to waiting media after being discharged from London’s King Edward VII’s Hospital the next day.