The King is set to welcome his fourth prime minister in less than four years, after Sir Keir Starmer succumbed to mounting pressure to quit.
In a rapid turnaround, Charles’s first premier was Liz Truss in 2022, followed by – just six weeks after his accession – Rishi Sunak, and then Sir Keir after a snap general election in 2024.
Demonstrating the changing nature of British politics, it was 11 years into Queen Elizabeth II’s reign before she welcomed her fourth prime minister, Sir Alec Douglas-Home in 1963.
As head of state, it is Charles’s duty to appoint the head of His Majesty’s Government – one of the few remaining personal prerogatives of the sovereign.
The monarch does not act on advice nor need to consult anyone before calling upon a politician to form a government.
But the overriding requirement is to appoint someone who can command the confidence of the House of Commons – which usually means the leader of the party with an overall majority of seats in the Commons.
Sir Keir and the King are said to have a warm rapport and a meeting of minds on social issues.
The Labour leader was appointed prime minister by Charles in July 2024 amid a difficult year for the King, just months after he was diagnosed with cancer.
The monarch – only two years into being head of state himself – sympathised with Sir Keir, telling him he must be “utterly exhausted and nearly on your knees” at their historic meeting at Buckingham Palace, and said getting to “grips with everything straight away” must be taxing.
As prime minister, Sir Keir has met the King most Wednesdays for a weekly audience to discuss Government matters following Prime Minister’s Questions, with the conversation usually taking place face to face.
Although the King must remain politically neutral on all matters, he is able to advise and warn his ministers – including his prime minister – when necessary.
The ongoing war in Ukraine, the crisis in the Middle East and US President Donald Trump are all likely to have been high on the agenda in recent times.
And the Government turned to Charles for his most challenging diplomatic test to date last month when he undertook a state visit to America.
The King charmed Mr Trump, delivered a powerful speech to Congress, and is seen as having repaired the strained UK-US special relationship, which appeared in jeopardy after Mr Trump repeatedly lambasted Sir Keir over the war in Iran.
When asked if it was awkward for Mr Trump to have a warmer relationship with the King than the prime minister, a senior palace aide said: “It’s not a competition between the King and the Government.
“The King is there to support the Government, to help the Government. It was at the Government’s request, of course, that he undertook this visit.”
Sir Keir has praised the King for his eco and social credentials, despite previously being in favour of the abolition of the monarchy.
In 2021, footage surfaced showing the then-human rights barrister telling a filmmaker in 2005: “I also got made a Queen’s Counsel which is odd, since I often used to propose the abolition of the monarchy.”
But when Elizabeth II died, he paid a warm tribute in the Commons to her “glorious” 70 years at the “heart of this nation’s life”.
He also spoke of the King’s new reign, hailing his environmental campaigning and commitment to “fairness”.
“King Charles III has been a devoted servant of this country his entire life, he has been a powerful voice for fairness, and understood the importance of the environment long before many others,” Sir Keir said.
Historian Ed Owens told the New York Times: “There’s a meeting of minds in terms of the social issues at stake.”
In 2025, Downing Street denied dragging the King into politics after Sir Keir joined Charles on a rare joint engagement to see a housing project.
The King took the PM and then deputy prime minister Angela Rayner on a visit to a Cornish development he inspired.
The joint trip came days before Sir Keir was expected to set out further measures as part of a pledge to build 1.5 million homes before the next general election.
In 2023, former director of public prosecutions Sir Keir, along with his wife Lady Victoria Starmer, was invited to a dine and sleep evening at Windsor Castle by the King, when he was leader of the opposition.
Charles and Sir Keir were seen engrossed in conversation at a reception in St James’s Palace before the Ukraine Recovery Conference in 2023, and photographed exchanging friendly greetings in the aftermath of the late Queen’s death.
Sir Keir was present at Elizabeth II’s funeral, the King’s accession council and his coronation, and he has also been a member of the Privy Council since 2017.
He joined the royal family in the royal box to watch the Platinum Jubilee Pageant celebrations in 2022, and was knighted by Charles, then the Prince of Wales, in 2014.
While he was the first Labour prime minister of the King’s reign, Sir Keir was also the first to be appointed by Charles as a result of a general election.
The King’s first premier was Liz Truss, who was already in place when he became monarch in September 2022, but her stint in charge was the shortest in British history.
Charles then welcomed Rishi Sunak as his second PM – also a Conservative – in October the same year, just six weeks after acceding to the throne.
