King Charles's III's cancer diagnosis splashed the front page of every British national newspaper Tuesday, with publications praising the monarch for revealing his illness and urging readers to rally behind him.

The Sun tabloid said Monday's shock announcement by Buckingham Palace, which sparked a flood of support from around the world, would heighten awareness about the condition.

"We should applaud Charles for choosing to reveal his cancer diagnosis in order to assist public understanding for those around the world who are affected by cancer," the tabloid wrote.

"Over the decades, His Majesty has been there for so many people, visiting hospitals and offering them hope," it added.

"Now it is time for the nation to show how much they care for him, which I am sure they will."

Charles, who became king upon the death of his mother, Queen Elizabeth II, on September 8, 2022, has generally enjoyed good health, barring injuries from polo and skiing.

But the palace said that during his recent hospital procedure for benign prostate enlargement "a separate issue of concern was noted" and that he had begun treatment.

Most papers carried portraits of Charles on their front page. The Sun went with "King: I have cancer" as its headline, while fellow redtop The Daily Mirror had "King's cancer shock".

The Daily Telegraph newspaper said the 75-year-old monarch's diagnosis should be "no cause for alarm" and that from all accounts "the prognosis is good".

"The key to dealing with cancer is to catch it early and that appears to have happened here," the newspaper wrote in an editorial.

The Times took a more sceptical tone, saying that by refusing to disclose the precise form of cancer, Buckingham Palace may well start the rumour mill churning.

"By chosing to be open one minute and not the next, they may well inspire unwanted speculation," the newspaper wrote.

"This strategy, however, runs the risk of leaving many people to assume that the King's condition is more sinister than the Palace is letting on."

The Guardian newspaper, less adoring of the British royal family than its rivals, said the king's diagnosis will "once again" raise questions about whether it is fair to expect a man in his mid-70s to "fulfil a rota of public duties".

"He in effect started his new job a decade after most men retire," the newspaper wrote.