British Prime Minister Theresa May is filing formal Brexit divorce papers today. 

Nine months after Britons voted to leave, May will notify EU Council President Donald Tusk in a letter that the UK really is quitting the bloc it joined in 1973.

In a statement in the Commons, the prime minister will then tell MPs this marks “the moment for the country to come together,” according to BBC.

It follows June's referendum which resulted in a vote to leave the EU.

Mrs. May's letter will be delivered today at 12:30 BST by the British Ambassador to the EU, Sir Tim Barrow.

The prime minister will have two years to settle the terms of the divorce before it comes into effect in late March 2019.

Tuesday night, Mrs. May reportedly spoke by telephone to Mr. Tusk, EU Commission President Jean-Claude Juncker and German Chancellor Angela Merkel.

Article 50 gives both sides two years to reach agreement, so unless both sides agree to extend the deadline for talks, the UK will leave on March 29, 2019.

Negotiations are expected to begin in mid-May.  The UK government says it wants to carry out both separation and trade talks at the same time, but EU chiefs say the two issues must be handled separately.

Reuters reports that a huge number of questions remain, including whether exporters will keep tariff-free access to the single market and whether British-based banks will still be able to serve continental clients, not to mention immigration and the future rights of EU citizens in the UK and Britons living in Europe.

Global banks such as Goldman Sachs are considering moving staff out of Britain due to Brexit, and some major companies and banks could use the Article 50 trigger date to update investors on their plans.