The King is facing regular treatment for cancer after his shock diagnosis was uncovered during his recent hospital stay.
Charles, 75, who has postponed all his public duties, returned to London from Sandringham on Monday and has already begun his medical care as an outpatient under the close supervision of his specialist team of doctors.
Buckingham Palace confirmed the King, who only acceded to the throne 17 months ago, does not have prostate cancer, despite having treatment for an enlarged prostate just over a week ago.
Further details of his condition have not been disclosed, and the Palace, which announced the news in a statement at 6pm on Monday, asked for privacy and only confirmed it is a “form of cancer”.
Charles was diagnosed after a “separate issue of concern was noted” and investigated while he was being treated for his benign prostate condition.
The Duke of Sussex has cleared his diary to fly to the UK to be with his father despite their troubled relationship, raising concerns about the seriousness of the King’s health.
Meanwhile, the Prince of Wales’s return to official duties this week, in the aftermath of the Princess of Wales’s abdominal surgery, was announced just hours before news of the King’s diagnosis, suggesting William is stepping up while his father is unwell.
William is likely to be undertaking some duties on his father’s behalf, it is understood, but Counsellors of State, who are appointed when a monarch cannot fulfil their duties as head of state, are not expected to needed.
The King will still be dealing with his red boxes of state business and official papers, and holding Privy Council meetings, which can be held via video, and weekly audiences with Prime Minister Rishi Sunak, which can take place over the phone.
Charles personally called both Harry and William, as well as his siblings the Princess Royal, the Duke of York and the Duke of Edinburgh, to give them the news before it was publicly announced.
This is the latest major royal health scare to hit the monarchy at the start of 2024, coming after the King’s hospital stay, Kate’s major surgery, keeping her away from official duties until after Easter, and Sarah, Duchess of York’s skin cancer diagnosis.
World leaders sent get well messages, with US President Joe Biden saying he was “concerned” and adding “I’ll be talking to him, God willing”.
Mr Sunak wished the King a full and speedy recovery, and Labour leader Sir Keir Starmer also sent a get-well message.
Buckingham Palace said the King remained “wholly positive” about his treatment and thanked his medical team for their swift intervention.
The Palace said: “During the King’s recent hospital procedure for benign prostate enlargement, a separate issue of concern was noted.
A statement from Buckingham Palace: https://t.co/zmYuaWBKw6
📷 Samir Hussein pic.twitter.com/xypBLHHQJb
— The Royal Family (@RoyalFamily) February 5, 2024
“Subsequent diagnostic tests have identified a form of cancer.
“His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties.
“Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual.
“The King is grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure.
“He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible.
“His Majesty has chosen to share his diagnosis to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer.”
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”.
She added: “The King’s openness about his battle with cancer is a powerful reminder that one in two of us may face cancer at some point in our lives.”
The Palace has called for the King’s privacy to be respected, especially during his treatment, but said he wanted to make his diagnosis public because of his long-running support for cancer charities.
The spokesman said: “The King has elected to make his diagnosis public once the schedule of treatment had begun, noting that as Prince of Wales he was patron of a number of cancer-related charities.
“In this capacity, His Majesty has often spoken publicly in support of cancer patients, their loved ones and the wonderful health professionals who help care for them.”
The Palace released a new unseen portrait of the King to accompany the announcement, showing him in a formal pose in a suit and tie with his hands behind his back during his state visit to France in September.
Charles was discharged from the London Clinic a week ago after undergoing a corrective procedure on his enlarged prostate.
The Queen, who visited the King each day and usually twice a day, will carry on with a full programme of official duties.
Charles was last seen on Sunday with Camilla at his side when he attended church in Sandringham.
He looked cheery as he waved at well-wishers.