Michael O'Leary hasn't shied away from criticism of Brexit, and has warned the impact on the airline industry could be substantial.
He said people were promised they could leave the EU and stay in the Single Market. "It's now absolutely clear that they were lied to by the exiters. That offer is not on the table and significant damage will be done to the UK economy as a result," he said.
The Ryanair boss is still hopeful the tide can be turned though, and that the referendum decision could be overturned altogether. "I don't have too much truck with these exiters saying, 'Oh, it's a sovereign vote and people have already voted out.' Rubbish," he said in an interview with the Sunday Times. "John Maynard Keynes was supposed to have said, 'When the facts change, I change my opinions.'"
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But with Theresa May saying she will press ahead with triggering Article 50 by the end of March, O'Leary has also thrown up a raft of warnings for the impact it will have.
And he's said that rival IAG could have more of a headache than most when Britain leaves the European Union. He pointed to global rules limiting foreign control of local airlines.
IAG, which owns Spain's Iberia and Ireland's Aer Lingus as well as British Airways, would, O'Leary says, be torn between Europe and Britain post-Brexit.
"All the other European carriers will go apeshit if IAG is allowed to simply circumvent the rule and have two European and a UK airline operating in the same group," he said, adding that he doesn't think IAG's structure "is going to survive".
In typical outspoken form, the Ryanair chief executive said IAG boss Willie Walsh was "talking rubbish" when he played down the effect leaving the EU will have on IAG.
Walsh said at the Airport Operators Association conference in November that there was no prospect of IAG being broken up in the wake of Brexit. He said the company had "tested and robust" structures in place to cope with restrictions on international ownership of airlines.
The IAG boss has also said his firm will continue to "press strongly" to maintain full access to international markets, warning that "anything short of an Open Skies [agreement] would be a massive retrograde step".
O'Leary also discussed his big plans for the budget Irish airline to become the "Amazon of travel". In December, Ryanair launched package holidays as its latest development, after launching Ryanair Rooms back in June to compete in the accommodation market.
"We don't want to be the innovator or explorer," O'Leary said. "We want to be the settlers. Somebody else can have the credit for the exploration. We want to go in and grab the land."