Donald Trump met the Prince of Wales for an afternoon tea at Clarence House but their meeting was cut short after the US President arrived late.
Charles and the Duchess of Cornwall welcomed Mr Trump and First Lady Melania at their official residence shortly before 6pm on Tuesday.
Protesters on the Mall could be heard and helicopters hovered above as the president’s motorcade arrived.
Rush-hour traffic meant Mr Trump and his wife Melania arrived around 40 minutes after they were expected for their half-an-hour sit down with Charles and Camilla, who greeted them at the entrance before welcoming them inside.
The two couples posed for pictures in the morning room before moving to private quarters for tea.
Both the duchess and Mrs Trump opted for bold colours, with Camilla wearing a red dress under a black cape jacket and the First Lady dressed in a yellow cape.
Their meeting was cut short as the couples were expected at a reception at Buckingham Palace hosted by the Queen a short time later.
Charles earlier met other Nato leaders, including Prime Minister of Canada Justin Trudeau, Prime Minister of Norway Erna Solberg and Prime Minister of Italy Giuseppe Conte.
Ms Solberg put the environment on the agenda as she gave the prince a football decorated with sustainability goals, telling him it is used to get young people to talk about the issue.
“I don’t know if you play football,” she joked as she gave the gift.
Charles replied: “A very, very long time ago.”
He threw the ball to a royal aide as he took Ms Solberg out of the morning room.
After the Trumps were last welcomed for tea at Clarence House on the president’s state visit to the UK in June, Mr Trump revealed he was pressed on climate change by Charles.
Mr Trump, who has previously accused climate experts of having a “political agenda”, told ITV’s Good Morning Britain he “totally listened” to the prince when the issue came up.
He said: “What he really feels one way about is the future.
“He wants to make sure future generations have climate that is good climate as opposed to a disaster, and I agree.
“I did mention a number of things, I did say the United States right now has among the cleanest climates.”