He said the EU was bouncing back a decade after the global financial meltdown
The European Commission president Jean-Claude Juncker has said Europe would "always regret" the Brexit vote, but insisted that "we will keep moving, because Brexit isn't everything".
During a state of the union address, Mr Juncker spoke about securing new EU trade deals with New Zealand and Australia, ruled out Turkey becoming a member and said a new migrant deportation policy would be proposed by the end of September.
Mr Juncker proposed a summit on 30 March 2019 - the day after Brexit takes place - in the Romanian city of Sibiu to map out the future of the EU with just 27 states.
He told the commission: "We have to respect the will of the British people. But we are going to make progress, we will keep moving, because Brexit isn't everything, it isn't the future of Europe."
To cheers from pro-Brexit members, including former UKIP leader Nigel Farage, he added: "I think you will regret it quite soon."
Mr Juncker said the European Commission will open free-trade negotiations with Australia and New Zealand and would aim to conclude talks with Mexico and South America trading bloc Mercosur by the end of the year.
He sounded a more bullish note, saying the bloc was bouncing back a decade after the global financial meltdown - with faster economic growth than the US.
Unemployment in Europe was at a nine-year low, he said, and the bloc was in the fifth year of an economic recovery that had finally reached every single member state.
He said: "The wind is back in Europe's sails. Now we have a window of opportunity, but it will not stay open for ever.
"Let us make the most of the moment: catch the wind in our sails."
Mr Juncker accused Turkey of distancing itself from the EU and said the country would not become a member of the bloc for the "foreseeable future".
He criticised Turkish President Recep Tayyip Erdogan and his government for the arrest of journalists and a crackdown following an attempted coup last year.
By the end of September, the European Commission will present a set of proposals on immigration that will focus on the return of those not eligible to stay in Europe and the opening of legal pathways to migration.
He said: "When only 36% of irregular migrants are returned, it is clear we need to significantly step up our work.
"This is the only way Europe will be able to show solidarity with refugees in real need of protection."
Mr Juncker also called for the roles of the president of the European Commission and the president of the European Council to be merged in future.