US President Joe Biden said he was “concerned” about the King’s cancer diagnosis, as foreign leaders wished him a swift recovery.

Mr Biden, who is six years older than the 75-year-old King, was asked by reporters whether he had a message for Charles during a visit to Las Vegas.

The President replied: “I’m concerned about him. Just heard about his diagnosis.

“I’ll be talking to him, God willing.”

Mr Biden later tweeted: “Navigating a cancer diagnosis, treatment, and survivorship takes hope and absolute courage.

“Jill and I join the people of the United Kingdom in praying that His Majesty experiences a swift and full recovery.”

His predecessor in the White House, Donald Trump, described the King as a “wonderful man”.

The frontrunner for the Republican party posted on his Truth Social platform: “King Charles has cancer.

“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!”

Canadian Prime Minister Justin Trudeau also offered his best wishes.

He tweeted: “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 one of the 14 Commonwealth realms where the King is head of state.

The leader of Commonwealth member Australia said his country’s thoughts were with the King and his family.

Prime Minister Anthony Albanese said: “Australians know that His Majesty King Charles has always reached out to us in our country’s toughest moments, showing kindness and care for those doing it tough.

“All of us are thinking of him and his family in this very hard time.

“We wish him well for a speedy recovery.”

Mr Albanese, who has said he believes an Australian citizen should replace the British monarch as the country’s head of state, recently put on hold a plan to hold a referendum on becoming a republic.

French President Emmanuel Macron tweeted: “Wishing His Majesty King Charles III a speedy recovery. Our thoughts are with the British people. Amities.”

President of Ireland Michael D Higgins “is very sorry and concerned to hear today’s statement regarding King Charles’ medical diagnosis”, according to a statement on his behalf.

“The president has sent his best wishes on behalf of the people of Ireland to King Charles for his medical treatment and for his full recovery, as well as to Queen Camilla and his family.”