The UK could re-join the EU after it splits from the economic and political bloc, Jean-Claude Juncker sensationally suggested on 10 March.
"I don't like Brexit because I would like to be in the same boat as the British. The day will come when the British will re-enter the boat, I hope," the EU Commission president told reporters in Brussels.
The comments, at a joint press conference with newly re-elected EU Council President Donald Tusk, came after an informal meeting of the other 27 leaders to prepare for the 60th anniversary of the Treaty of Rome.
Tusk, for his part, warned against a "multi-speech" EU.
"Considering the interest of the community of 27 countries in Europe in the context of the upcoming Brexit negotiations as well as the long-term strategic interest of the EU, I will be urging everyone to strive to maintain political unity among the 2... All 27 leaders agree with this objective," the Polish politician said.
May restated her promise to invoke Article 50 of the Lisbon Treaty and trigger two-year-long Brexit talks.
"It is time to get on with leaving the European Union and building the independent, self-governing, global Britain the British people have called for," the UK prime minister said at the EU Council meeting on 9 March.
"And so, as I have said, we will trigger Article 50 by the end of this month. This will be a defining moment for the UK as we begin the process of forging a new role for ourselves in the world – as a strong country with control over our borders and over our laws.
"And as the Chancellor made clear yesterday, we will use this moment of change to build a stronger economy and a fairer society that works for ordinary working people by embracing genuine economic and social reform here at home.
"Britain is leaving the European Union but we are not leaving Europe. A global Britain that stands tall in the world, will be a Britain that remains a good friend and ally to all our European partners."
But the Article 50 bill is facing parliamentary ping-pong between the House of Commons and Lords. That is because the peers backed two amendments to the draft legislation.
The changes, if passed in the Commons, would make the government hold a "meaningful vote" on the final Brexit deal in Parliament and force ministers to unilaterally guarantee the residency rights of the more than three million EU nationals in the UK.