Messages of support have come from unlikely sources after revelations of the King’s surprise cancer diagnosis.

News of his illness has also opened up speculation about a royal rapprochement as the monarch’s estranged youngest son, Prince Harry, reportedly rushes from California to London to be with his father.

Buckingham Palace confirmed late on Tuesday (British time) that the 75-year-old monarch would begin immediate regular treatment for cancer, and would postpone public duties.

He will continue with constitutional and state duties, including his weekly meetings with British PM Rishi Sunak.

Tweet from @AlboMP

The disease was detected late last month, when the King spent three days in hospital for treatment for an enlarged prostate. Neither his exact cancer diagnosis nor his prognosis has not been confirmed.

“During the King’s recent hospital procedure for benign prostate enlargement, a separate issue of concern was noted. Subsequent diagnostic tests have identified a form of cancer,” the palace said.

“His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties.”

The palace said the King had chosen to share his diagnosis to prevent speculation and in the hope it might “assist public understanding for all those around the world who are affected by cancer”.

“He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible,” it said.

But he is expected to have a prolonged period away from public duties and there is no confirmation of when he will return.

Prime Minister Anthony Albanese said the news, which came just 17 months after the King ascended the throne on the death of Queen Elizabeth, was difficult.

“All Australians will be sending their best wishes to King Charles for a speedy recovery,” he said in Canberra on Tuesday.

“We want to see His Majesty return to full duties as soon as possible.

“We have invited King Charles to visit Australia and we sincerely hope that is able to occur.”

The King was expected to tour Australia in late 2024, as part of a broader trip to the region for the Commonwealth Heads of Government Meeting in October in Samoa.

Opposition Leader Peter Dutton urged men not to delay visits to the doctor.

“We wish every best wish to King Charles … he’s a stoic individual,” he said.

“There’s a message the palace wants to get out as well … make sure you go and have a check-up because early detection is important.”

Other world leaders offered their own good wishes. They included US President Joe Biden, who is expected to speak to the King in coming hours.

Tweet from @POTUS

European leaders also sent messages, as did Canadian Prime Minister Justin Trudeau.

“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,” Trudeau wrote on X.

There were also other, perhaps less expected, good wishes. One came from British anti-monarchy organisation Republic.

Tweet from @RepublicStaff

And there was another from former US president Donald Trump.

“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!” he wrote on his Truth Social platform.

Elsewhere, there were reports the King personally told his oldest son, Prince William, and his siblings of his illness. He also reportedly called Prince Harry – thought to be the first time in months father and son have had any contact.

A source close to Harry said he would fly to Britain from his home “in the coming days”. There are multiple reports he is already on his way to London.

Wife Meghan Markle and the couple’s children, Archie and Lilibet, are expected to remain in the US.

-with AAP