Britain’s ambassador to the European Union, Sir Ivan Rogers, unexpectedly resigned from the post on Tuesday, giving no reason for his decision.
His resignation came just three months before Prime Minister Theresa May is due to start formal Brexit talks.
Rogers was appointed by former prime minister David Cameron as Britain's permanent representative to the EU in November 2013.
He was one of the Britain's most experienced diplomats on EU affairs.
The resignation is the second by a senior British EU official in the wake of the negotiations. Britain's European commissioner Jonathan Hill also stepped down in June.
TRT World's Jack Parrock is following the story from Brussels.