Gavin Williamson has been sacked as defence secretary, following reports that he allegedly revealed secret information from an important government meeting. He strongly denies that he did this.
Prime Minister Theresa May wrote a letter asking him to step down from his job, saying she'd "lost confidence in his ability to serve".
The job is an important position in Mrs May's group of top ministers called the cabinet.
Mr Williamson has been accused of revealing the contents of government discussions around allowing Chinese phone company Huawei to help build the UK's new 5G network, reported in the Daily Telegraph.
The discussion took place in a top secret government meeting called the National Security Council on 23 April.
There has been no official confirmation of Huawei's role in the 5G network and the government has said a final decision would be made at the end of spring.
In a letter to Mr Williamson, the prime minister said the leak from the meeting was "an extremely serious matter and a deeply disappointing one".
She said an investigation into the leak of information provided "compelling evidence suggesting [his] responsibility for the unauthorised disclosure".
Mrs May went on to ask him to leave the government.
In his reply, Mr Williamson, who has been defence secretary since 2017, said: "I appreciate you offering me the option to resign, but to resign would have been to accept that I, my civil servants, my military advisers or my staff were responsible: this was not the case."
Gavin Williamson will be replaced by Penny Mordaunt - the first ever woman to become the defence secretary.
She had been the international development secretary, but Prisons Minister Rory Stewart will now take over that job.