Standing on Buckingham Palace's west terrace, Trump and first lady Melania Trump watched as rows of redcoated soldiers arrayed themselves across the palace's garden.
The Trumps then visited Westminster Abbey, where they laid a wreath at the Tomb of the Unknown Warrior.
After Trump inspected the honor guard, the Trumps and Windsors stood at the entrance as a band played "God Save the Queen " before they went inside for a private lunch, which was attended by Prince Harry.
On Monday, Trump arrived in Britain with his wife Melania for a three-day visit, and he had already blasted Khan before his plane touched down.
With Trump's arrival generating plans for massive street protests, the provocative greeting-similar to the giant "Baby Trump" blimp which has become so popular in recent years-is additional evidence of how reviled and little-respected the president is among many in Britain.
The group behind "Trump Baby", which appeared during last year's protests, had vowed to fly it again if they could raise at least £30,000 (about $50,000) for anti-racism and climate change charities.
Judi said the President of the United States produced a "toe-curlingly awkward" visit when he met with the Queen a year ago.
In a newspaper column on Sunday, Khan said Trump was "one of the most egregious examples of a growing global threat" from the far-right to liberal democracy.
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In a tweet, President Trump described the London Mayor as a "stone cold loser" who had been "foolishly nasty" to him.
Trump is to remain in the United Kingdom from Monday to Wednesday, which comes at a tumultuous time in British politics, with Prime Minister Theresa May due to step down on Friday.
The Trumps arrived at London Stansted Airport before departing for the USA ambassador's residence.
The centerpiece of the president's European trip will be two days to mark the 75th anniversary of the June 6, 1944, D-Day landing, likely the last significant commemoration most veterans of the battle will see.
Then, following the terrorist attack on London Bridge and Borough market in 2017, the President accused Mr Khan of "pathetic" behaviour.
Supporters of the invite say that the U.S.
He praised May's Brexit-supporting rival, former foreign minister Boris Johnson, saying he would be a "great" potential prime minister and also called for arch-Brexiteer Nigel Farage, a scourge of May's ruling Conservative Party, to conduct talks with the EU.
During the banquet, both the US President and the Queen are expected to make a speech.
Sadiq Khan, the UK-born son of Pakistani immigrants, has given the go-ahead for the huge "Baby Trump" balloon to fly again, following last year's viral debut.
Trump said in an interview with The Sun last week that Markle was "nasty" about him - a claim which he denied, despite the paper posting a recording of the interview.