The King has begun treatment for a cancer diagnosed following his treatment for an enlarged prostate.
He will now undergo a schedule of regular treatments, during which he has been advised by doctors to postpone public-facing duties.
Buckingham Palace has not confirmed what type of cancer the King has.
Follow live: King chose to share diagnosis to ‘prevent speculation’
Here are some of the previous health issues the King has faced.
Enlarged prostate
The King’s health has been in the spotlight already this year.
On 17 January, he was diagnosed with a benign condition while staying at Birkhall in Aberdeenshire, after going for a check up because he was experiencing symptoms.
He underwent surgery for the enlarged prostate, and it is understood he wanted to share the news to encourage other men to get themselves checked.
The NHS reported huge boosts in people asking to find out more about the condition affecting the King.
The King, who only acceded to throne 16 months ago, cancelled engagements and was urged to rest by his doctors ahead of the corrective procedure.
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One in every three men over the age of 50 will have symptoms of an enlarged prostate, which include needing to visit the toilet more frequently, with more urgency, and difficulty emptying the bladder.
An enlarged prostate, known as benign prostatic hyperplasia, does not usually pose a serious threat to health, and it is not cancer.
Knee surgery
In March 1998, the King – then Prince Charles – had laser keyhole surgery on his right knee.
The outdoor and active Prince of Wales also suffered from back pain at the time, which had been aggravated over years of playing polo.
Double arm break
The King has over the years had some form for falling from his horse in a polo game.
In June 1990 he broke his arm in two places and spent three nights in Cirencester Memorial Hospital in Gloucestershire after an accident in a competitive game of polo.
When he left hospital, he was reported to have told journalists outside “you can all go home at last”, as he got into his car.
He needed another operation three months later after one of the fractures didn’t properly heal.
It is understood bone was taken from his hip to help with healing the break, while a metal plate was also fitted with screws.
Shoulder fracture
In January 2001, he fractured a bone in his shoulder after falling off his horse during a fox hunt in Derbyshire.
He had to wear a sling for several days while the fracture healed.
‘Minor injury’
Just a few months later, in August, he was taken to hospital for what was described as a minor injury.
It is reported he fell halfway through the second half of a charity polo match in Cirencester in Gloucestershire.
Hernia operation
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Going back to March 2003, the King had a routine operation for a hernia, and reportedly joked afterwards “hernia today, gone tomorrow”.
It’s not clear how he picked up the injury, which is a common operation.
