On Wednesday, the UK prime minister is scheduled to 'trigger' Article 50 of the Treaty on European Union to announce to the 27 other EU member states that the UK intends to leave the union.
It will be no surprise. On June 23 last a majority of voters in the UK and Gibraltar voted in favour of leaving. On October 2, Theresa May announced her intention to 'trigger' Article 50 before the end of this month. Everyone saw this trigger being primed.
If the UK changes its mind - and states do (Norway changed its mind twice about joining the EU and Indonesia changed its mind about leaving the UN) - then it will also be largely forgotten.
At one level, nothing changes with the triggering of Article 50.
The UK is still bound by EU law - emphasised recently by the European Parliament - and, legally, it is 'business as usual' with the UK obliged to comply with EU law, while businesses and citizens in the UK may avail of EU rights and others elsewhere may still invoke EU law against the UK.
In reality, though, the shadow boxing is over.
The hard negotiations start. There will be even more uncertainty and volatility. The court challenges will continue - Mrs May's government has lost in the UK Supreme Court already which means that challengers may take heart.
Many commentators assume the UK will leave the EU exactly two years from the triggering of Article 50. It is not so simple.
The EU treaties would normally cease to apply to the UK from the date of entry into force of the withdrawal agreement concluded between the EU and the UK - which could be earlier or later than two years after the triggering notification.
However, if no such agreement is reached then the EU treaties would cease to apply to the UK exactly two years after the notification to leave.
But this rule is also subject to an exception. The 27-member European Council (without the UK), may, in agreement with the UK, unanimously decide to extend this two-year period. So, even the 'two year' rule is not so certain or simple.
By triggering Article 50, the UK is left out of the negotiations on the EU side - a situation that it is getting used to over the last few months as the '27' develop their own strategy in meetings from Bratislava to Brussels.
Could the UK withdraw the notification and change its mind? Views differ whether this is legally possible but, on balance, the UK could change its mind and the 'law would probably follow the politics' and allow it to stay.
That might happen if there could be sufficient reform in the EU to win a majority vote in the UK to remain.
If the UK leaves and decides to rejoin the EU then it has to apply in the normal way to join the EU according to Article 50 (5). If the UK leaves the EU but Scotland or Northern Ireland wanted to join the EU then they would first have to be states (or become part of states) to be able to join the EU by virtue of the forgotten Article 49.
The negotiations will be long and tense. This is the style of many EU negotiations.
And to cap it off, the departure of a big state - indeed, any state - is entirely unprecedented stuff.
The negotiations will be late. The EU rarely reaches agreement on time, not to mind, ahead of time. The negotiations will be tough. Interests differ radically between the parties. Talks cover the most difficult of issues including money, sovereignty, pride, trade and people.
The UK wants to concentrate on trade, but most of the 27 prioritise the EU vision, people, money and, as part of the mix, trade. Even the 'divorce bill', estimated by some EU sources at up to €60bn but which the UK reckons is much less, will be a flashpoint.
The challenge in the EU 2019 deal is to avoid the Versailles Treaty 1919 problem of concluding a treaty which is unduly tough on one state - it was on Germany in 1919 and should not be on the UK in 2019 - but equally, Brussels will not want to make the EU too easy to leave or to enable those who leave to prosper better than those who remain.
Depending on the arrangement concluded, there is a possibility that Ireland may even need a referendum, which means that the UK's future could be partially in Irish hands.
Triggering Article 50 was the easy bit: the EU is like a lobster pot - easy enough to enter but difficult to leave.
Dr Power is a partner in A&L Goodbody