US President Donald Trump has fired Secretary of State Rex Tillerson via Twitter, naming CIA Director Mike Pompeo as his replacement.
Mr Tillerson's spokesman said he only learned he was out of a job when he saw the president's tweet thanking him for his service as top US diplomat.
The former ExxonMobil chief had a series of public rifts with the White House since he was appointed last year.
Mr Trump also named Gina Haspel to become the CIA's first female director.
What was Trump's reason?
Speaking to reporters outside the White House on Tuesday, Mr Trump said his differences with Mr Tillerson came down to personal "chemistry".
"We got along actually quite well, but we disagreed on things," said the president.
"When you look at the Iran deal, I think it's terrible. I guess he thought it was OK.
"I wanted to either break it or do something and he felt a little bit differently, so we were not really thinking the same.
Media captionTillerson - I will now return to private life
"With Mike, Mike Pompeo, we have a very similar thought process. I think it's going to go very well.
"Rex is a very good man, I like Rex a lot."
Mr Tillerson is the latest in a long list of senior officials who have either resigned or been fired since Mr Trump took office.
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How was Tillerson fired?
The Department of State said Mr Tillerson had not spoken to the president and was "unaware of the reason" for his firing.
Under Secretary Steve Goldstein said: "The Secretary had every intention of staying because of the critical progress made in national security."
Mr Goldstein himself was fired later on Tuesday by the White House.
Mr Tillerson said later in a news conference that he had received a call from the president on Air Force One after midday, about three hours after Mr Trump fired him via tweet.
He added he would finish his term on 31 March and would "return to private life as a private citizen".
According to the Associated Press, White House chief of staff John Kelly called Mr Tillerson on Friday and advised him to watch out for a presidential tweet about him.
Mr Kelly did not tell Mr Tillerson when the tweet would be posted or what it might say, reports the news agency.
The secretary of state was on an official tour of Africa last week when he was caught unawares by Mr Trump's agreement to meet North Korean leader Kim Jong-un.
The top US diplomat's team said he was feeling unwell on Saturday and later in the weekend the state department said he would cut short his tour by a day.
"I felt like, look, I just need to get back," Mr Tillerson told reporters on his plane home, reports the Washington Post.
The 65-year-old arrived back in Washington before dawn on Tuesday to learn he was out of a job a few hours later.