Video report by ITV News Washington Correspondent Robert Moore
President Trump has sacked Rex Tillerson as secretary of state, telling reporters he had made the decision "by myself", and that Mr Tillerson would be "much happier" out of the role.
Mr Tillerson, who in just over a year at the state department has frequently found himself on the wrong side of the president, is to be replaced by CIA Director Mike Pompeo.
Characteristically, Mr Trump first announced the move on Twitter, and it appeared this might have been the first his top diplomat had heard of it.
The president later firmed up the announcement in an official statement, saying he was "confident" that CIA director Pompeo was " the right person for the job at this critical juncture".
Senator Bob Corker, who chairs the Senate's foreign relations committee and has been one of Mr Tillerson's most vocal supporter on Capitol Hill, said the president's decision had come as a surprise, although he acknowledged there had "been tensions" between the two men.
Speaking to journalists, Mr Trump said he had "got along well with Rex [Tillerson]" but that the two "disagreed on things" and did not see eye to eye on issues including Iran.
Earlier it appeared another issue over which the two might be at odds was whether Russia could be linked to the poisoning of former Russian spy Sergei Skripal in Salisbury, as Britain asserts.
Mr Tillerson sided with the UK, pointing the finger at Moscow while Mr Trump initially held back, although the president later backed the UK's position.
Mr Tillerson's responsibilities will be handed to his deputy at the end of the day and he will leave his post formally at the end of the month.
In a brief address, Mr Tillerson thanked those he had worked with at the state department and the American people, and pointedly made no reference to Mr Trump.
He singled out two accomplishments he felt had been achieved on his watch - the isolation of North Korea, which he said had "exceeded expectations", and efforts in Afghanistan to push the Taliban towards peace talks.
But he acknowledged that "much work remains" as regards Syria, Iraq and the global campaign against so-called Islamic State.
Mr Trump said that he and Mr Tillerson had discussed the former ExxonMobil boss's exit from the role, but some reports said Mr Trump's tweet was the first Mr Tillerson knew of it.
A report in The Washington Post said Mr Tillerson was told of his impending removal last Friday.
The president is said to have wanted to make the change ahead of planned talks with North Korean leader Kim Jong-un.
In a further twist, Steve Goldstein, the under secretary of state, who suggested Mr Tillerson had not been consulted before he was sacked, was himself fired shortly after the reports circulated.