The video was shot during a reception at Buckingham Palace on Tuesday night, hours after Trudeau and Trump met on the sidelines of a gathering of leaders from the North Atlantic Treaty Organisation military alliance.
Mr. Trump's press conference would have served as counter-programming to an impeachment hearing that's getting underway on Capitol Hill. "It's really, honestly, it's a disgrace", he told reporters.
New York Magazine contributor Yashar Ali, along with other news outlets, also pointed out a fifth person who appears to be Princess Anne, daughter of Queen Elizabeth II.
Johnson, meanwhile, professed ignorance when asked by reporters about the conversation.
"He was late because he takes a 40-minute press conference off the top", Trudeau said at one point.
Macron nodded, as Trudeau replied, "He was late because he takes a ..." U.S. President Donald Trump described the remarks as "very, very nasty".
After a working lunch with the leaders of nine nations that meet or exceed the 2% goal, another hot mike moment heard him boast: "That was amusing when I said that guy was two-faced". "But you know the truth is that I called him out on the fact that he's not paying 2 per cent, and I guess he's not very happy about it". He's not paying 2 per cent, and he should be paying 2 per cent.
"It's Canada. They have money". "I was happy to take part in it but it was certainly notable".
Asked about the video, Mr Johnson told reporters: "It's complete nonsense".
"We were all surprised and I think pleased to learn that the next G-7 will be at Camp David, I think that was an unscheduled announcement", Trudeau said as he sought to downplay his comments.