After 3½ years of moving deadlines, dire warnings and a baffling new language of Brexiteers, Brextensions and Brexit border backstops, the long-awaited moment has arrived.
Friday marked a rare consummation of a tumultuous process that will redefine Britain's place on the world stage.
But the certainty of Brexit Day will do little to address the doubts, fears and speculation over what comes next.
So let's go through the biggest questions:
What is Brexit?
A blend of Britain and exit, Brexit is the all-encompassing nickname for the United Kingdom's withdrawal from the European Union.
The process is broadly divided into two parts — the divorce (or withdrawal agreement), and the future relationship (or non-binding political declaration).
After Brexit, it will be up to the two sides to negotiate the particulars of their new relationship.
What is happening today?
At 23:00 GMT (or 6 p.m. ET) on Jan. 31, the United Kingdom officially ceased to be a member of the European Union.
After 47 years of membership, the British flag was lowered at the European Parliament as the EU 28 became the EU 27. Seventy-three British MEPs will lose their jobs, after less than a year in office.
WATCH: Members of the European Parliament sing and tear up after Brexit vote
In Britain, many of those in favour of the separation said they would fly the British flag; others said they would light a candle in their windows to represent their flickering hope this could all be reversed one day.
Notably in London, the moment was not marked by the bongs of Big Ben. Elizabeth Tower remains under construction, and Prime Minister Boris Johnson said it would cost more than $850,000 to temporarily restore the "clapper" mechanism in time.
How did we get here?
Johnson famously said he would rather be "dead in a ditch" than delay Brexit beyond Oct. 31, 2019.
Months later, it was a matter of "deep regret" for Johnson that another extension was needed. Parliament had refused to pass Johnson's deal, and bound by a new law created just for the purpose, the U.K, prime minister was forced to ask Brussels for a further extension.
Johnson soon called a snap election and readily won a clear majority after campaigning on the slogan: "Get Brexit done." The votes soon followed.
How did we really get here?
In a referendum on June 23, 2016, nearly 52 per cent of U.K. voters who cast ballots chose to leave the EU. Then-prime minister David Cameron had promised the country a chance to settle the long-simmering European question once and for all.
Cameron resigned the next day.
Years of political wrangling followed, amid massive demonstrations for and against Brexit. Brexiteers argued the U.K. was now duty-bound to carry out the will of the people. Remainers demanded a second referendum (sometimes People's Vote), arguing the narrow majority would collapse after voters learned the true consequences of leaving.
WATCH: CBC's Margaret Evans and Thomas Daigle reflect on Brexit coverage
What happens next for the relationship?
The divorce deal sets out the immediate consequences of the split over a range of issues, including trade, citizens' rights and health care.
In most cases, those real consequences are deferred by the 11-month "Transition Period" (sometimes "Implementation Period") during which Britain continues to contribute to the EU budget and be bound by EU rules.
What if there's no deal by the end of 2020?
It's not out of the question: the European Union says the 11-month negotiating time frame is not nearly enough to negotiate a new trade deal, and France's Europe minister warns a chaotic cliff-edge, no-deal exit scenario is entirely possible at the end of 2020.
Under the terms of the divorce deal, the sides can agree to a one-time extension of one to two years, but such an agreement must be made before July 1, 2020.
Without an extension or a deal in place by the end of the year, borders could be closed, tariffs could be imposed and a wide range of rules and regulations affecting millions of people could change overnight.
What about Northern Ireland?
Northern Ireland voted 55.8 per cent in favour of remain. In the time since, its border has become one of the thorniest issues for negotiators.
The Republic of Ireland and Northern Ireland share the only land border between the U.K. and the EU. When the transition period ends, any goods or people crossing over will be subject to whatever trade and entry regulations have been negotiated.
But the border is an intensely sensitive issue. The physical border was all-but dismantled following the Good Friday Agreement that brought an end to decades of violence that killed thousands of people.
Any proposal that would create a hard border with customs and immigration checks has already brought threats of a return to violence. No side wants a hard border.
Prime Minister Johnson discarded his predecessor's approach of negotiating a backstop arrangement for the border that would go into force, preventing a hard border, until a new deal could be negotiated.
His new Irish Protocol creates an effective customs border between Great Britain and Northern Ireland. Goods deemed to be "at-risk" of importation into Ireland would be subject to customs, with refunds offered where the goods remained in Northern Ireland.
That has stoked the ire of loyalists in Northern Ireland who oppose any division with Great Britain that would make Irish reunification more likely.
In 2016, six in 10 Scottish voters cast their ballot to remain in the European Union.
Now facing the prospect of being forced out of the EU against its will, the Scottish independence movement has surged, even promising an independent Scotland could seek an eventual return to EU membership.
Scotland's First Minister Nicola Sturgeon won a symbolic vote in the Scottish legislature demanding that Boris Johnson call a second referendum on independence. Prime Minister Johnson has so far flatly rejected the possibility.
WATCH: Scottish First Minister calls for Independence Referendum
What will this mean for Canada?
After seven years of negotiations, Canada's trade deal with Europe, CETA, went provisionally into force in 2017. It will continue to regulate trade between Canada and the EU Bloc. Post-Brexit, Canada will need to negotiate a new deal or arrangement to govern trade with Britain.
Pressure will mount for Canada to secure a new trade deal with its third-largest trading partner, which sees an annual bilateral exchange of nearly $30 billion of goods.
Canada has pledged to take full advantage of the opportunity to renegotiate this particular bilateral trade relationship and pledged to seek a "seamless transition" of CETA.
What else should I know?
Despite the cost-saving promises of the Brexiteers, Britain will be asked to pay the equivalent of more than $50 billion to settle its obligations with the bloc.
Britain's desire and newfound freedom to negotiate a bilateral trade deal with the U.S. could be complicated by Britain's decision this week on Huawei. The U.S. has pleaded with Britain to cut the Chinese telecommunication manufacturer out of its next generation 5G network. China meanwhile, has threatened to pull its investments in the U.K. if Huawei is barred.
During the transition period, British citizens and those from EU countries will continue to enjoy free movement. After the transition, those who have been living continuously in one country for five years will be given permanent residence; those with less will be given the right upon reaching five years.
The U.K. government has posted a country-by-country guide for those abroad.
Watch: 'Brexit begins' from CBC News: The National
With files from CBC News, The Associated Press and Reuters