Sir Mark Ivan Rogers on Tuesday resigned from his post as the United Kingdom’s ambassador to the European Union, reported BBC. He was appointed to the post by former British Prime Minister David Cameron in 2013.

The UK Foreign Office said they will not divulge further details about his resignation at the moment. His tenure was supposed to end in November 2017.

Brexit select committee head Hilary Benn said Roger’s resignation had come at a “crucial” time. The Labour MP also asked the government to find a replacement soon. British Prime Minister Theresa May had said that she would start Brexit talks by March end.

The UK had voted to leave the EU in a referendum on June 24, 2016, after which David Cameron, who had campaigned for the country to remain in the bloc, resigned as prime minister. The UK government had rejected a petition calling for a second referendum. May took charge on July 11 to implement the result of the vote along with her team.