He believed that Britain would soon "regret" their decision.
He also issued a warning to Britian, which is now slowly progressing with exit negotiations, saying that "we will always regret this, and I think you will regret this too, soon". Juncker declared that "Brexit isn't everything" and it was not the "be all and end all".
But the most detailed and principled attack on Juncker's plans came from Harald Vilimsky, of Austria's Freedom Party, which prompted Juncker to leave mid-speech.
European Commission President Jean-Claude Juncker proposed combining the Commission and Council presidencies - a move that would transform the EU leadership and consolidate authority in a single figure who would campaign for the post. But we are going to make progress.
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.
While past year it had been plain to see the EU was "battered and bruised", he said, now the union was "slowly but surely gathering momentum".More news: Trump Commission Meeting to Restrict YOUR Voting Rights — HAPPENING NOW
He wrote: "2016 was in many ways an "annus horribilis" for the European project". The right road for Europe can only be the road where there is more democracy left to the people, more democracy left to the citizens where people can vote whether or not they want to have Schengen maintained or not, whether they want their borders or not.
"All but two member states are duty bound to join the Euro area".
"It is high time to bring Romania and Bulgaria into the Schengen area".
Turkey got a sharp reminder that European Union membership is nowhere in sight as a result of growing EU concerns about President Recep Tayyip Erdogan's crackdown on political opponents and his bashing of countries in the bloc.
Juncker gave an insight into his vision for the EU's future and how he hopes to keep the other 27 member states together after a tumultuous period.
"The message is very clear: Brexit has happened, new steam ahead..."More news: Jaguar Land Rover just made a huge commitment to electrification
The minister would be in charge of economic and financial issues not only for the euro zone, but for all EU countries, Juncker said in a state of the union speech to the European Parliament.
"You have learned nothing from Brexit". "We will move on because Brexit isn't everything".
"We are working towards an ambitious free trade deal and securing a deep and special partnership with the European Union".
Speaking on Sky News, the politician was asked if he thought the United Kingdom would in fact "regret" Brexit, which was backed by 17.4million people.
Mr Corbyn's spokesman said: "Labour has from the time of the referendum last summer said we respect and accept the referendum result".More news: Will Alexis Sanchez take this good advice on Arsenal career?