Tim P. Whitby/Getty Images

Nearly four years after the UK voted to leave the European Union, Brexit has finally happened.

As the clock struck 11.00.p.m. GMT, the Article 50 process by which a member state leaves the EU expired and the UK has now entered the transition process it agreed with the bloc. For the first time ever, the EU is down a member state. It's a monumental moment that will go down in history, for better or worse.

So what happens now?

In the short term, the biggest changes will be invisible to the public. During the transition period, currently set to expire on December 31 of this year, the UK will continue to obey EU laws and European courts. Businesses will be able to operate as normal and people wanting to travel around the EU will not be affected.

However, Brexit is far from done. Before the transition period ends 11 months from now, the UK will try and negotiate a deal with Brussels on their future relationship. Failure to reach an agreement would mean the hardest Brexit possible, causing economic damage for both sides and possibly the wider world. This is a scenario that both sides are eager to avoid.

These negotiations will begin on March 3. In the meantime, both parties will work to establish their priorities and red lines. The UK will probably want to have its cake and eat it: near-frictionless trade with the EU while enjoying the freedom to do as it pleases at home and strike trade deals with the wider world.

For the EU, the priority will be keeping the UK as close to EU regulations as possible and protect European interests. And if you thought phase one of Brexit was nasty, phase two is going to be even worse.

The UK now enters a new phase in its history. The choices that Boris Johnson takes in the coming months will have huge implications for British citizens and for people far beyond the UK's borders. However, he does so standing alone.

The next Brexit deadline is already hurtling towards us. And for the UK more than anyone else, to get what it wants could require shutting its eyes and hoping for the best.