The UK's ambassador to the US described the White House as "inept", "incompetent" and "uniquely dysfunctional" in leaked Foreign Office memos dating from 2017 to the present.
President Trump has hit back, telling reporters: "We're not big fans of that man."
But who exactly is "that man" and how did he rise to prominence to hold one of the most prestigious jobs in the diplomatic service?
Who is Sir Kim Darroch?
Sir Kim is considered something of a veteran in the diplomatic arena, with a career spanning three decades.
He joined the diplomatic service in 1977 after graduating from Durham University with a degree in zoology.
Between 2007 and 2011 he served in Brussels as the UK Permanent Representative to the European Union, representing UK interests in areas such as the aftermath of the financial crisis and the issues around European integration.
He was secretary of the National Security until September 2015 and led on issues such as the rise of Islamic State in Iraq and Syria, Russian aggression in Ukraine, the nuclear threat from Iran and the collapse of government authority in Libya.
Prior to taking on the role of UK ambassador to the US in January 2016, the 65-year-old served as national security adviser to former prime minister David Cameron.
What other controversy has surrounded Sir Kim?
Shortly after President Trump's election win, the Sunday Times reported on a secret memo in which Sir Kim apparently suggested the UK could exploit Mr Trump's character and inexperience in office.
The memo said: “The president-elect is above all an outsider and unknown quantity, whose campaign pronouncements may reveal his instincts, but will surely evolve and, particularly, be open to outside influence if pitched right.
“Having, we believe, built better relationships with his team than have the rest of Washington diplomatic corps, we should be well placed to do this.”
The following week, the president declared in a late-night tweet that Nigel Farage would do a "great job" and "many people" wanted to see him as the UK's ambassador in the US.
Number 10 was forcd to insist there was "no vacancy" and praised Sir Kim for being an "excellent ambassador."
In his first interview after the controversy, Sir Kim changed tact and hailed Mr Trump’s "historic and impressive" election victory and called the so-called special relationship between the US and the UK “stronger than ever."
What else has Sir Kim said about the president?
Despite the UK ambassador saying in order to communicate with Mr Trump "you need to make your points simple, even blunt", he spoke highly of the president in an interview with Financial Times last year.
The diplomat gave Mr Trump a ringing endorsement, saying: "I have met him seven or eight times and always found him to be absolutely charming."
What has Donald Trump said about Sir Kim?
In reaction to the leaked memos from the Foreign Office, Mr Trump, dismissed the ambassador, saying "we're not big fans of that man."
"He has not served the UK well," the president added.
"So I can understand it, and I can say things about him, but I won't bother."
The next prime minister can elect a new UK ambassador to the US, but according to ex-defence secretary Sir Michael Fallon, Sir Kim's term was "coming to an end" anyway.