On Tuesday evening, the Canadian and UK prime ministers and French president Emmanuel Macron were caught on a hot mic appearing to gossip about the US president’s lengthy press conferences.
Mr Johnson is heard asking Mr Macron, who had had a separate bilateral meeting with Mr Trump: “Is that why you were late?”
Canadian PM Mr Trudeau responds: “He was late because he takes a 40-minute press conference off the top.”
Other words were exchanged but could not be heard, before Trudeau added with a chuckle: “I just watched his team’s jaws drop to the floor.”
Although Mr Trump, who faced protests upon arrival at the reception, was not named directly in the conversation, the US president had held a long unscripted press conference earlier that day.
Asked on Wednesday about what he thought of the video and Mr Trudeau specifically, Mr Trump said: “Well, he's two-faced. And with Trudeau – he’s a good guy – but the truth is I called him out on paying 2% (to the Nato budget) and I guess he’s not very happy about it.
“He’s not paying 2% and he should be paying 2%. It's Canada, they have money. But that’s the way it is, I can imagine he’s not that happy.”
Mr Trudeau later sought to downplay the incident, saying he had a “great meeting” with Trump when asked if had apologised to the president.
He added: “We were all surprised and I think pleased to learn that the next G7 will be at Camp David, I think that was an unscheduled announcement and... I think every different leader has teams who every now and then their jaws drop at unscheduled surprises, like that video itself for example.”
Mr Trump also said his scheduled press conference had been called off and he would go directly to Washington after his meetings instead.
The footage came after Mr Trump said comments Mr Macron had made calling Nato "brain-dead" were "very nasty" before the pair’s meeting at the US ambassador's residence in London. Mr Trump also pressed Mr Trudeau on Canada's Nato spending at another bilateral meeting.
Trump holds court
Earlier on Tuesday, the US president had attacked Mr Macron, Barack Obama and the Democrats in a long press conference.
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He spent around 40 minutes taking questions from the press – particularly from organisations he has blamed for negative coverage in the past.
He chose to take multiple questions from the New York Times – a publication he frequently attacks as "fake news" on Twitter – asking if he would see positive stories about him in the publication.
It was a far cry from recent fraught press conferences in the US when Mr Trump has resorted to hissing at news organisations and questions he does not like.
When asked about the upcoming British election, he claimed he was not getting involved, saying "I don't want to complicate it", before boasting of all the US electoral candidates he had helped win seats in midterm elections.
The President also denied claims the US was eyeing up the NHS, saying: "We wouldn't want it even if it was offered to us on a silver platter.”
When asked about Labour leader Jeremy Corbyn, he said: "I can work with him. I'm a very easy man to work with.”
The president also used the time to attack the current impeachment proceedings against him and criticise Mr Macron for comments about Nato.
He used questions on Syria to boast of the US's killing of Isis leader Abu Bakr Al Baghdadi – an achievement he wants to be seen as equal to that of the assassination of Osama bin Laden.