There were handshakes all around, and then the threesome stood side-by-side as a military band played the American national anthem.
The US President and the First Lady, Melania Trump, flew via helicopter Marine 1 from London to Windsor before being driven along the Long Walk and into the castle where Her Majesty was waiting for the pair on the dais in the Quadrangle.
Trump then took a turn with the Queen to inspect the Guard before the whole party headed inside for afternoon tea.
Though it's unclear why the Queen appeared unamused, Friday was far from the first time she has met a US president.
Trump was gracious about the British sovereign in a newspaper interview out Friday in which he attacked Prime Minister Theresa May's strategy on Brexit. "As offensive as Trump was, he was not actually as late as everyone thought". I really look forward to meeting her.
"You could see that suppressed dominance where he felt that he had to still motion to her".
The heads of state are meeting over tea for 30 minutes before Mr Trump departs England for a weekend in Scotland.
Trial starts of technology which aims to catch drivers on the phone
Although the signs are unable to log offending number plates, such a feature is being considered for development in the future. The Council's Road Safety Team and local company Westcotec have worked together to develop and deploy the system.
Steve Kingstone, the Queen's Media Secretary, and Sally Osman, the Director of Royal Communications, have recently assisted the Royal Family with the media frenzy surrounding Meghan Markle's absence from her wedding to Prince Harry.
"That wouldn't be required from a head of state or the wife of a head of state", he said. Mary Anne MacLeod Trump, who emigrated to the U.S.in 1930, died in 2000.
The meeting comes just one day after Trump arrived in London for his four-day visit.
Mr Trump, who is known for clasping visitors' hands and pulling them towards him, shook the monarch's hand briefly, and did not bow at the same time. "Come on Kate!" he wrote.
Prince Charles is a keen environmentalist.
The rest of Donald and Melania Trump's visit with Queen Elizabeth appeared to continue smoothly. Royal commentator Victoria Arbiter, who works for CNN, Trump's least favourite news network, insisted he was on time.