European Commission chief Jean-Claude Juncker has voiced his hope that Britain will one day return to the EU fold despite voting to leave.
Mr Juncker made the comments a day after Theresa May attended an EU summit in Brussels - the last time a British Prime Minister is set to do so with Britain a full member of the union.
The other 27 leaders are continuing the talks without Mrs May, looking at the future of the bloc after Brexit.
"I do not like Brexit because I would like to be in the same boat as the British," Mr Juncker said.
"The day will come when the British will re-enter the boat, I hope."
But, he added, "Brexit is not the end of the European Union, nor the end of all our developments, nor the end of our continental ambitions."
Mrs May plans to trigger Article 50 of the Lisbon Treaty - starting formal divorce procedures - by the end of the month.
But some European diplomats expect it to come as early as next week.
EU leaders have said they will be ready to respond within 48 hours of receiving notification that Article 50 had been triggered.
"We are well prepared for the whole procedure and I have no doubt that we will be ready within 48 hours, I think it is a proper time to react," EU President Donald Tusk told a news conference.
The response would also include convening a special summit at which the EU leaders would agree broad negotiating guidelines in the divorce talks with London.
The EU is facing an uncertain future, between Brexit and a string of elections in European nations, including France and Germany, that will have a significant impact on the bloc.
The leaders will gather in Italy this month to mark the bloc's 60th anniversary and map out its post-Brexit strategy.
"The motto is that we are united in diversity," said German Chancellor Angela Merkel.
But even as the leaders attempted a show of unity, differences lingered.
Western countries, led by Germany and France, want deeper integration, at least among some states and in certain areas, leading to the prospect of a two-speed union.
Eastern nations such as Poland do not want to cede any more national sovereignty to Brussels, and oppose the idea of different levels of integration within the bloc.