Britain's ambassador to the United States, Kim Darroch, resigned on Wednesday after a series of leaked diplomatic cables revealed he had told 10 Downing Street that the Trump administration was "inept" and "clumsy", CNN reports.
The resignation, announced by the UK Foreign Office, came after US President Donald Trump declared on Monday that the White House would no longer deal with Darroch.
The ambassador made his decision to step down after seeing that Boris Johnson, the current frontrunner to replace Theresa May as British Prime Minister, had refused to support him during Tuesday night's leadership debate, a British government official confirmed to CNN.
CNN reached out to sources close to Darroch for comment, but has not had a response.
Foreign Office minister Alan Duncan told the BBC on Wednesday that Johnson had thrown the former ambassador "under the bus" by refusing to back him.
In the cables, leaked to the Daily Mail newspaper, Darroch warned the UK government that Trump's "career could end in disgrace," and described conflicts within the White House as "knife fights."
British Prime Minister Theresa May said Wednesday it was a "matter of great regret" that Darroch had felt it necessary to resign and that the government owed him an "enormous debt of gratitude."
"Good government depends on public servants being able to give full and frank advice," May told the House of Commons during Prime Minister's Questions.
"I want all our public servants to have the confidence to be able to do that. And I hope the house will reflect on the importance of defending our values and principles — particularly when they are under pressure," she added.
Following the leak, Darroch was disinvited from a dinner with Trump, the Emir of Qatar and Treasury Secretary Steven Mnuchin which took place on Monday night. The ambassador also pulled out of a meeting between Ivanka Trump and UK International Trade Secretary Liam Fox on Tuesday.
British Foreign Secretary Jeremy Hunt, who is standing against Boris Johnson for the leadership of the Conservative party, tweeted Wednesday that he "profoundly" regretted how an "outrageous leak" had caused Darroch's resignation.