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BRUSSELS, BELGIUM - MARCH 29 : Britain's ambassador to the EU Tim Barrow (L) delivers British Prime Minister Theresa May's formal notice of the UK's intention to leave the bloc under Article 50 of the EU's Lisbon Treaty to European Council President Donald Tusk in Brussels on March 29, 2017. (Photo by Dursun Aydemir/Anadolu Agency/Getty Images)

BRUSSELS, BELGIUM - MARCH 29 :  Britain's ambassador to the EU Tim Barrow (L) delivers British Prime Minister Theresa May's formal notice of the UK's intention to leave the bloc under Article 50 of the EU's Lisbon Treaty to European Council President Donald Tusk in Brussels on March 29, 2017.  (Photo by Dursun Aydemir/Anadolu Agency/Getty Images)