King Charles has been diagnosed with cancer and began treatment on Monday, Buckingham Palace says
The Palace says the cancer was identified during the King's recent hospital treatment for a benign enlarged prostate
"A separate issue of concern was noted," the Palace says, and "subsequent diagnostic tests have identified a form of cancer"
The Palace has not said what type of cancer the King has been diagnosed with
Prince Harry has spoken to his father and will travel to the UK from the US in the coming days
Charles, 75, has been advised to postpone public duties, but will "undertake state duties" and continue to meet Prime Minister Rishi Sunak weekly
He is being treated as an out-patient, and is at home in London on Monday night, the Palace says
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Follow King's 'relentlessly upbeat' lead, Jennie Bond says
Former BBC royal correspondent Jennie Bond says the King's diagnosis is shocking and sad, but he is taking a "relentlessly upbeat" lead.
Image source, PA MediaThe King was seen in public only yesterday, heading to church in Sandringham with Queen Camilla
It's just gone two hours since Buckingham Palace released the news that King Charles has been diagnosed with cancer. Here's what we know so far:
Image source, PA MediaCamilla promised to pass on well wishes at the event
Queen Camilla has long been the patron of Maggie's cancer charity and was present at the opening of a new centre in the Royal Free hospital in London last week.
She promised well-wishers to pass on hopes the King would make a speedy recovery after receiving treatment for an enlarged prostate.
It's understood the engagement was in the diary before the King's diagnosis and the Queen decided to continue with it as planned.
The King will continue to meet Prime Minister Rishi Sunak weekly despite his cancer diagnosis, the BBC understands.
It is understood that suitable arrangements will be made if the King's doctors advise him to minimise in-person contact.
The King is also expected to remain available for state duties, including for meetings of the Privy Council, the body of ministers and advisers that keep him up-to-date on the workings of the government.
He will continue to receive and review official red boxes of government paperwork, it is understood.
Image source, Getty Images
Image source, Getty ImagesTV presenter Carol Vorderman talks to King Charles - then Prince Charles - at an event in 2013
As well as politicians, celebrities have been sharing their best wishes to the King.
British former boxer Frank Bruno was one of the first to post a message online after the news broke. "Thoughts and prayers with him and the Royal Family," he writes. "When are we ever to be rid of this evil disease cancer?"
TV broadcaster Carol Vorderman writes on X, wishing him a speedy recovery, and expressing "particular thoughts for everyone who's suffering with cancer or waiting for treatment right now".
Football presenter Gary Lineker says he is "really sorry" to hear the "awful news", adding: "Wish him a full and speedy recovery."
And actor David Suchet, best known for playing Belgian detective Hercule Poirot for 25 years, says it is "wonderful that he has shared his cancer diagnosis so openly".
"My wife, Sheila, joins me in wishing King Charles III a very speedy recovery to full health."
The BBC's royal correspondent, Nicholas Witchell, says the Royal Family will "step up" to cover the King's public duties - listen to his analysis here.
King Charles: Members of the Royal Family will 'step up'
Image source, ReutersCanadian Prime Minister Justin Trudeau says on X: "I, like Canadians across the country and people around the world, am thinking of His Majesty King Charles III as he undergoes treatment for cancer.
"We're sending him our very best wishes – and hoping for a fast and full recovery."
Canada is a member of the Commonwealth and the King remains its head of state.
Image source, ReutersFormer US President Donald Trump has described the King as a "wonderful man".
Writing on social media, Trump says: "He is a wonderful man, who I got to know well during my presidency, and we all pray that he has a fast and full recovery!"
Image source, ReutersUS President Joe Biden has said he is "concerned" following the King's diagnosis.
Asked by reporters whether he had a message for the King, Biden said: "Yes, I’m concerned about him.
"I just heard his diagnosis. But I'll be talking to him God willing."
We've been receiving more reaction from politicians.
The leader of Northern Ireland's Democratic Unionist Party, Jeffrey Donaldson, wrote on X that he was sending the King "every good wish as he commences his treatment", while Ulster Unionist Party leader Doug Beattie said the news was "shocking" and he sent his "heartfelt wishes".
"This is, unfortunately, a reality many families, right across these islands, face day and daily," he said.
And the Mayor of London, Sadiq Khan, wished the King "a speedy and full recovery" on behalf of Londoners.
"I look forward to his return to full health as soon as possible."
Image source, ReutersIt's understood that King Charles informed his immediate family of his diagnosis personally.
This includes his sons Prince William and Prince Harry, and his siblings Princess Anne, Prince Andrew and Prince Edward.
Former UK PM Boris Johnson says on X: "The whole country will be rooting for the King today. Best wishes to Charles III for a full and speedy recovery."
Liz Truss, another former PM, also sends her best wishes and adds: "He will be in our thoughts and prayers. God Save The King!"
Liberal Democrat leader Sir Ed Davey has also just shared his reaction to the news.
In a message posted on X he wrote: “The Liberal Democrats join the rest of the nation in wishing a full and quick recovery to His Majesty.”
Earlier, another of the party's MPs, Sarah Olney, was in the House of Commons when the news broke and said: "I'd just like to express on behalf of myself and my Liberal Democrat colleagues our sympathies to the King and to his family, and of course our hopes that his treatment should prove to be successful."
The US has just responded to the news of the King's diagnosis.
US State Department Spokesman Vedant Patel describes it as “incredibly sad news" and adds: "I’m very sorry for the King and his family".
He tells a briefing of reporters that the Biden administration’s thoughts are with the King and the Royal Family.
On Sunday morning, King Charles attended church with Queen Camilla in Sandringham, Norfolk - his first public outing since his three-night hospital stay a week ago.
He's now returned to London from Norfolk where he's beginning treatment.
Image source, PA Media
Image source, PA MediaIf you're just joining us, or need a quick recap, here's everything we currently know about the King's cancer diagnosis:
Image source, Buckingham Palace
Image source, ReutersNorthern Ireland's Deputy First Minister Emma Little-Pengelly says she will be praying for the King.
"I would like to wish His Majesty, King Charles all the very best for his treatment," she says.
"I, like many people throughout Northern Ireland, will keep him and his family in my prayers."
The first and deputy first ministers of Northern Ireland hold a joint office and have equal power.
Image source, PA MediaNorthern Ireland's First Minister Michelle O'Neill says she is "very sorry" to hear of the King's diagnosis.
"I am very sorry to hear of King Charles' illness and I want to wish him well for his treatment and a full and speedy recovery," she says.
It comes just two days after O'Neill became the first nationalist to be appointed first minister.
Image source, ReutersPrince Harry has spoken to the King about his cancer diagnosis and will travel from California to the UK to see him in the coming days, the BBC has been told.
King Charles will continue to undertake state business while he receives treatment, Buckingham Palace says.
We know that this includes reviewing dispatches from the government and signing official documents.
It is just the public-facing engagements that the King is postponing.