At a Press conference later in the grounds of the PM's country residence, Mr Trump insisted he "didn't criticise" the Prime Minister and hit out at "fake news".
On the day before the news conference, the British tabloid The Sun published an interview with Mr. Trump in which he said he thinks Boris Johnson would make a great prime minister, and Britain's trade relationship with the US could come to an end if British Prime Minister Theresa May follows through with the so-called "soft" Brexit blueprint.
Trump, who prides himself on never apologizing, came close to offering something of an apology for his unvarnished remarks.
Trump backed away from his criticism of how May is handling Britain's exit from the European Union.
"She said: 'Don't worry it's only the press.' I thought that was very professional". But he acknowledged that Brexit is a "very complicated negotiation and not an easy negotiation, that's for sure".
"We have this stupidity going on, pure stupidity, but it makes it very hard to do something with Russia because, anything you do, it's like: "Russia, oh he loves Russia", Mr Trump said at the press conference before news of the indictment.
Even May's political opponents-outside her own party-seem to be outraged about Trump's attack on her. "I actually told Theresa May how to do it but she didn't agree, she didn't listen to me", he said. While he spoke highly of Johnson, he also heaped praise on May, calling her an "incredible woman" who is "doing a fantastic job". Then he left to have tea with Queen Elizabeth II at Windsor Castle.
The Queen, the president and first lady Melania Trump all shook hands. Just days after lobbing thunderous broadsides at his British hosts, Trump was on his best behaviour as he capped his two-day visit to the United Kingdom by dropping by Windsor Castle for tea with the Queen.
May likewise glossed over the comments in The Sun.
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Mr Trump is due to meet Vladimir Putin, who has rejected the nerve agent claims, at a summit when he finishes his four-day visit to Britain.
In an interview with The Sun, Trump said May's long-awaited blueprint for Brexit, published this week, would "probably kill" any future trade deal between the U.S. and U.K. He also said May's arch-rival Boris Johnson-who resigned as foreign secretary on Monday in protest at the blueprint-would "make a great prime minister".
May's advisers said that the news conference was a welcome relief - and that the trip was salvaged from disaster.
He also said Boris Johnson would make a "great prime minister". Trump explained his comments to the Sun about Johnson in terms of himself, as he often does.
He said the paper's story was "generally fine", but "it didn't put in what I said about the prime minister, and I said tremendous things". He's been very nice to me.
"He's been saying very good things about me as president".
In a statement ahead of Trump's arrival, she said the visit would focus on trade and strengthening defence and security ties, saying there was no stronger alliance than Britain's "special relationship with the US". "But maybe they're taking a little bit of a different route, so I don't know if that's what they voted for".
"I read reports where that won't be possible, but I believe after speaking with the prime minister's people and representatives and trade experts it will absolutely be possible".
May, standing at a lectern beside Trump, disagreed.