He spoke about why he believed Brexit was "a waste of time and energy"; why he was confident that no other member states would follow the UK's lead in quitting the bloc; and why he regretted not having intervened in the 2016 referendum campaign, Financial Tribune reported.
"This is a sad day for the European Union, it’s a tragedy in history," former EU Commission president Jean-Claude Juncker said. "But Britain is a great nation, British people have inspired so many positive undertakings in the world that I will never have disrespectful feelings for Britain."
The country on Saturday began an uncertain future outside the European Union, hours after the historic end to almost half a century of EU membership was greeted with a mixture of joy and sadness.
There were celebrations and tears across the country as the EU's often reluctant member became the first to leave an Organisation set up to forge unity among nations after the horrors of World War II.
Almost nothing will change straight away, because of an 11-month transition period negotiated as part of the exit deal.
Britons will be able to work in and trade freely with EU nations until December 31, and vice versa, although the UK will no longer be represented in the bloc's institutions. But legally, Britain is out.
Thousands of people waving Union Jack flags packed London's Parliament Square and sang the national anthem to mark that reality at the moment of Brexit at 11 pm (2300 GMT) Friday—midnight in Brussels.
As UK Prime Minister Boris Johnson—a figurehead in the seismic 2016 referendum vote for Brexit—held a private party in his Downing Street office, a clock projected on the walls outside counted down the minutes to departure.
In an address to the nation, he hailed a "new era of friendly cooperation" with the EU while Britain takes a greater role on the world stage.
Johnson acknowledged there might be "bumps in the road ahead", but predicted the country could make it a "stunning success".
"The most important thing to say tonight is that this is not an end but a beginning," he said in a televised address.
However, Brexit has exposed deep divisions in British society, and many fear the consequences of ending 47 years of ties with their nearest neighbors.