King Charles III has been diagnosed with a form of cancer, says Buckingham Palace.
It is not prostate cancer but was discovered during his recent treatment for an enlarged prostate.
The type of cancer has not been revealed, but according to a palace statement, the King began "regular treatments" on Monday.
Buckingham Palace says the King "remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible."
He will postpone his public engagements and it is expected other senior royals will help to stand in for him during his treatment.
No further details are being shared on the stage of cancer or a prognosis.
The King, 75, returned to London from Sandringham in Norfolk on Monday morning and the palace says he has commenced treatment as an outpatient.
Although he will pause his public events, the King will continue with his constitutional role as head of state, including paperwork and private meetings.
There is a constitutional mechanism for when the head of state is unable to carry out official duties - in that circumstance "counsellors of state" can be appointed to stand in for the monarch.
At present that includes Queen Camilla, Prince William, Princess Anne and Prince Edward, with Prince Harry and Prince Andrew no longer to be called on as non-working royals.
Prince William had also temporarily withdrawn from public engagements while he helped his wife Catherine, the Princess of Wales, as she recovered from "abdominal surgery".
But it was announced earlier on Monday he would return to public duties later this week.
The Duke of Sussex has spoken with the King and will travel to the UK to see him in the coming days, BBC News has been told.
The King was seen at a church service in Sandringham on Sunday, where he waved to crowds.
He had a prostate procedure at a private London hospital more than a week ago.
The King had chosen to go public about his prostate treatment, with the aim of encouraging more men to get prostate checks, the palace said at the time.
He was said to have been delighted to have raised awareness about the issue with the NHS website reporting a surge in issues about prostate conditions.
For many types of cancer, the chance of getting it increases with age. UK figures suggest, on average each year, more than a third (36%) of new cancer cases were in people aged 75 and over.
Prime Minister Rishi Sunak wished the King a "full and speedy recovery", alongside Labour leader Sir Keir Starmer.
Read full statement:
Latest Stories
-
Miss USA Noelia Voigt resigns title on mental health grounds
9 mins -
Ama Sey blames me for her defeat in the NPP Primaries – Kate Gyamfua
11 mins -
Zenith Bank’s 2024 quarter one profit up 41%; boosted by loan, asset and deposit growth
11 mins -
Nana Ama Mcbrown to host Ghana to the World concert in USA
35 mins -
It’ll be good if Bawumia is elected President – Ahafo Regional House of Chiefs President
42 mins -
Anti-Gay bill: Supreme Court grants Richard Sky’s request to amend suit
42 mins -
Procurement chamber trains private contractors and suppliers on accurate tender procedures
48 mins -
Otumfuo’s words have been key – Kotoko forward Mukwala on team’s resurgence
52 mins -
We created a room for Botsio to be comfortable – Azamati on running third leg
56 mins -
EC’s limited voter registration got off slowly due to inadequate publicity – Otokunor
57 mins -
T-bills: Government borrowed GH¢15.60bn in April 2024
1 hour -
Two busted for attempting to smuggle 130 bags of cocoa beans to Togo
1 hour -
April 2024 inflation declines marginally to 25 percent
1 hour -
Ian Gelder: Game of Thrones actor who played Kevan Lannister dies aged 74
2 hours -
Current players of Kotoko do not deserve to play for the club – Augustine Ahinful
2 hours