The King has been admitted for treatment on his enlarged prostate at the same hospital where the Princess of Wales is being cared for after abdominal surgery.
Charles as seen entering the private London Clinic in central London on Friday morning with the Queen at his side.
He took time to visit his daughter-in-law Kate, who is on the 11th day of her hospital stay after undergoing a successful major operation last week.
A Buckingham Palace spokesman said: “The King was this morning admitted to a London hospital for scheduled treatment.
“His Majesty would like to thank all those who have sent their good wishes over the past week and is delighted to learn that his diagnosis is having a positive impact on public health awareness.”
It is not known how long the King will spend in hospital or the exact nature of his treatment.
He was dressed in a smart suit and tie and navy overcoat for his arrival at the hospital, while Camilla was wearing a royal blue coat and carrying a green handbag.
Charles arrived back in London from Norfolk on Thursday afternoon ready for the procedure, after squeezing in a couple of behind the scenes official duties.
The Court Circular recorded the King received Dame Polly Courtice, emeritus director of the University of Cambridge Institute for Sustainability Leadership, and Professor Robert Miller, director of the Whittle Laboratory, on Thursday morning at Sandringham.
In a picture released on the royal family account on X on Friday, he was shown lighting a candle with the Queen earlier this week to mark Holocaust Memorial Day. Charles issued a message ahead of the commemorations, describing it as “a valuable opportunity for the richly diverse communities of this nation to come together and recommit to building a society free from antisemitism, persecution and hatred”.
Charles was diagnosed with the benign condition on January 17 while staying at Birkhall in Scotland, after going for a check-up because he was experiencing symptoms.
He is understood to have wanted to share the news to encourage other men to get themselves checked.
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.
The Queen had previously said her husband is “fine” and looking forward to getting back to work.
News of his diagnosis came on the same day that Kensington Palace announced the princess was in hospital after undergoing abdominal surgery.
Kate, 42, is not expected to carry out official engagements until after Easter, with the Prince of Wales clearing his diary of official duties for the time being.
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.
But patients may need to have several tests for the condition to rule out the possibility they have another illness with similar symptoms, such as prostate cancer.
Surgery is usually only recommended for moderate to severe symptoms that have not responded to medicine, the NHS website says.
Treatment can include a number of procedures, including removing part of the prostate gland with a laser, water ablation using the pressure of the water to destroy prostate tissue, or urethral lift implants, which hold the enlarged prostate away from the urethra so it is not blocked.
Other options include a prostate artery embolisation, during which tiny plastic particles are injected into blood vessels to shrink the prostate gland by reducing its blood supply.
NHS England said the “enlarged prostate” page on the NHS website received one visit every five seconds on the day the King’s diagnosis was announced, with further huge boosts in visits in the days that followed.
Published: by Radio NewsHub