Britain begins the day as a member of the European Union. Its status at the end of the day as a proud nation that has reclaimed its sovereignty, or a diminished presence in Europe and the world will still be up for debate.
Britain officially departs the EU at 11 pm local time Friday, midnight in Brussels (2300 GMT, 6 pm EST).
The departure comes 3 years after the country voted by a margin of 52%-48% to walk away from the club that it had joined in 1973.
It's the first time a country has left the EU, and many in the bloc regard it as a sad day.
In Brussels, European Council President Charles Michel and EU Commission leader Ursula von der Leyen are due to sketch out the EU's first steps as a group of 27, rather than 28.
UK Prime Minister Boris Johnson is to meet in the morning with his Cabinet in the pro-Brexit town of Sunderland, in northeast England.
He is scheduled to deliver a televised address to the country an hour before departure, calling Brexit "not an end but a beginning."
According to his office, he will describe it as "a moment of real national renewal and change."
Mayor Sadiq Khan, who has linked the Brexit vote to a rise in xenophobic abuse, said Britain's capital would remain "a truly global, European city."
"And we will continue to welcome people from around the world, regardless of the color of their skin, the color of their passport or the colors of their national flag."
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