Updated: Jan 26
The heads of the European Commission and Council - Ursula von der Leyen and Charles Michel - have signed the Withdrawal Agreement, ahead of the UK's exit from the EU on 31 January.
The Queen approved it on Thursday, and next Wednesday the European Parliament is expected to vote for it too. The UK has agreed to abide by EU rules during a transition period until the end of the year. By 2021 the UK aims to have agreed a deal on future ties.
Brexit ends 46 years in the EU club.
After the document was signed in Brussels it was taken to Downing Street by EU and UK officials, for signing by UK Prime Minister Boris Johnson, due later on Friday.
The agreement will then travel back to Brussels, and a copy of it will remain in London.
Next week's European Parliament vote is seen as all but a formality, after it was backed by the parliament's constitutional affairs committee on Thursda
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Mrs von der Leyen and other senior EU figures are sceptical about the UK government's plan to negotiate a comprehensive deal on future relations before the end of 2020. They believe the timetable for that is too tight.
But Prime Minister Boris Johnson is upbeat, insisting the UK can now move forward after years of wrangling over Brexit.
Charles Michel, the former Belgian Prime Minister who chairs EU summits, said in a tweet "things will inevitably change but our friendship will remain.
"We start a new chapter as partners and allies."