EU leaders will meet to discuss their Brexit battle plans on 29 April, European Council President Donald Tusk has announced.
Setting the date for the remaining 27 members of the bloc to discuss their negotiating strategy, Mr Tusk said the process of "divorcing" the UK must be the "least painful for the EU".
His announcement comes after Theresa May confirmed she would trigger Article 50, officially notifying the EU of the UK's intention to leave, on 29 March.
The date Mr Tusk has set is the soonest the 27 could hold a summit to discuss their response.
Making the announcement, he said: "As you all know, I personally wish the UK hadn't chosen to leave the EU, but the majority of British voters decided otherwise.
"Therefore, we must do everything we can to make the process of divorce the least painful for the EU.
"Our main priority for the negotiations must be to create as much certainty and clarity as possible for all citizens, companies and member states that will be negatively affected by Brexit, as well as our important partners and friends
around the world."
Speaking at Prime Minister's Questions last week, Mrs May said she did not want Brexit to be referred to as a "divorce" because divorces were often followed by poor relationships.
Mrs May told the Cabinet on Tuesday morning that her letter to the EU giving notification of the UK's intention to leave would be "one of the most important documents in our country's recent history".
A Downing Street spokesman said Mrs May had told her ministers the letter would "set the tone for our new relationship with Europe and the world".
It suggests the letter could give significant detail of the UK's intentions for negotiations rather than simply informing them of the UK's exit.
The EU has been impatient for the Government to trigger Brexit since the referendum. However, it was held up by a court battle which forced Mrs May to put the issue to a vote in Parliament.
Mrs May's European counterparts had urged her to avoid triggering Article 50 at the same time as the Treaty of Rome celebrations on 25 March.
However, the date for the summit will come in the middle of the French presidential elections.
Negotiations are not expected to begin in earnest until May or June when the EU is expected to raise the issue of an exit bill for the UK, which has been put as high as €60bn (£51bn).
There have been concerns it could become a roadblock to discussions, with warnings that EU leaders will play "hardball" with "British dosh".
Speaking in Swansea on Monday, after the 29 March date was disclosed, Mrs May said she would be "negotiating hard, delivering on what the British people voted for".
Other significant areas of discussion include the rights of EU citizens living in the UK and Britons living in Europe, and whether the EU is prepared to thrash out a trade agreement at the same time as the Brexit deal.
EU negotiator Michel Barnier has made clear he wants Brexit talks to be completed by October 2018 to give time for any agreement to be ratified before the UK leaves.
Under the two-year Article 50 process that would make Brexit day 29 March 2019.