The day Article 50 was triggered
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Article 50 triggered: The story of the day

29 March 2017 Last updated at 17:09 BST

Nine months after adults in the UK voted to leave the European Union, the Prime Minister Theresa May has officially told EU leaders the UK is on its way out.

Martin went to the Belgium capital, Brussels, which is home to the European Union headquarters.

Watch his report about the day Article 50 was triggered.