Speaking after talks at Chequers, the prime minister's country residence, Mr Trump said the US-UK relationship was "the highest level of special", while Mrs May said they had discussed plans for an "ambitious" trade agreement.
"I used to love London as a city", Trump said. "I have a lot of respect for the prime minister", Trump said.
"I said Brexit will happen and it did happen", he added. "But when they make you feel unwelcome, why would I stay there?" he said.
But on Friday, Trump said that after speaking with May and her advisers he had been convinced a trade deal "absolutely will be possible".
Yet supporters of Brexit see a US trade deal as a central plank of their strategy: Vote Leave, the campaign to leave the European Union, said post-Brexit trade deals centering on the United States could create 284,000 jobs.
In his interview with The Sun, Trump slammed May over her "soft" Brexit plan, which has put May's standing as the head of the Conservative Party in jeopardy.
When asked of her views on the Access Hollywood tape, May said, "I think that's unacceptable, but in fact Donald Trump himself has said that and apologized for it".
According to The Sun, Trump said May not only ignored the advice he gave her on Brexit, but has gone "the opposite way", leading to "very unfortunate results".
Trump also wants changes to the interior of the plane, too.
May echoed that, saying, "I think we have already struck up a good relationship".
The Reverend Nigel Sinclair, a 53-year-old Church of England preacher, came in what he called his Sunday vicar's outfit, carrying a sign that showed how Trump's ideas differ from those of Jesus Christ.
The president stood behind his comments to The Sun regarding immigration, saying it was "changing the culture. As he said in his interview with the Sun she "is a very good person" and he 'never said anything bad about her, '" White House Press Secretary Sarah Sanders said. There is nothing to suggest the hard-nosed dealmaker would go easier on Britain, and he may press hard for lower tariffs and easier access for United States industry to Europe's second-biggest economy.
"The UK can't afford to alienate either the U.S. or the European Union, its two largest foreign trade partners, and will not be able to choose an "either-or" solution", commented Fiona Cincotta, senior market analyst at City Index in London. Mr. Trump's intervention was "very important, because if you can't do a trade deal with your closest ally, then who can you do a trade deal with?" said Jacob Rees-Mogg, a Tory MP who has been among the sharpest critics of Ms. "My wife is a tremendous fan of hers", Trump said.
The Trumps entered the castle's Quadrangle by Range Rover after arriving on the castle grounds by helicopter. The queen navigated her way around him.
The Trumps European trip continues with a weekend trip to Scotland before arriving in Helsinki, Finland, for a highly anticipated summit with Russian President Vladimir Putin. "And I think if I were president then, he would not have taken over Crimea", Trump said, fending off a tough question about Putin's annexation - the main point of contention for North Atlantic Treaty Organisation allies - by essentially blaming his predecessor.
Mr Trump's first visit official visit to the United Kingdom as president took place in between the North Atlantic Treaty Organisation summit in Brussels and a meeting on Monday in Helsinki with Russian leader Vladimir Putin. You take a look at your hospital in London, you know what I'm talking about, with all of the disgusting things going on there with all of the crime that's being brought in.
That was why the government's white paper was "veiled by strategic ambiguity on trade in goods", said Hosuk Lee-Makiyama, director of the European Centre for International Political Economy in Brussels.