Boris Johnson has wished King Charles a "speedy recovery".
The former UK Prime Minister has taken to social media to send his best wishes to the 75-year-old monarch, who has been diagnosed with "a form of cancer".
Johnson, 59 - who served as the UK Prime Minister between 2019 and 2022 - wrote 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 UK Prime Minister, has also sent her best wishes to the King, who ascended to the throne in 2022 following the death of Queen Elizabeth.
The 48-year-old politician - who was the Prime Minister from September to October 2022 - wrote on X: "Sending every best wish to His Majesty The King and the Royal Family as he undergoes his treatment for cancer. He will be in our thoughts and prayers.
"God Save The King! (sic)"
Buckingham Palace announced the news of Charles' diagnosis on Monday (05.02.24).
The Palace also confirmed that the King has already begun his cancer treatment and that he will continue to undertake "state business and official paperwork as usual".
Meanwhile, Dickie Arbiter - the King's former media manager - has suggested that the monarch will be frustrated by the nature of his cancer treatment.
He told the BBC World Service: "He is pragmatic about it and he is upbeat and he’s carrying on work as usual, albeit on an administrative capacity rather than being seen out and about.
"And that’s the part that will frustrate him because that’s his job; to be seen out and about by the great British public, by the people of the Commonwealth, by the people of the realms, by business, by industry, by parliamentarians and he’s not able to do that."