Donald Trump has cancelled a press conference at short notice after world leaders including Boris Johnson were captured on film apparently talking about him behind his back.
The US presidents decision to leave the UK-hosted Nato summit without talking to the media is also likely to be cheered by the Conservative Partys campaign team, who feared he could damage their election hopes.
The US president lashed out after Trudeau was caught alongside Johnson and Emmanuel Macron seemingly gossiping about Trumps late appearance for an engagement at the gathering of world leaders.
He was late because he takes a 40-minute press conference off the top, Trudeau said.
Later in the conversation Trudeau adds: You just watched his teams jaws drop to the floor.
Trump, who has been at pains not to endorse Johnson in the UK election as the Tory prime minister fears it could be damaging, could not resist hitting back, claiming Canada was not meeting its Nato obligations to spend 2% of GDP on defence.
Hes two faced, Trump said as he held talks with German chancellor Angela Merkel.
And honestly with Trudeau, hes a nice guy, I find him to be a very nice guy.
But the truth is I called him out on the fact that hes not paying 2% and I guess hes not very happy about it.
You were there, a couple of you were there, and hes not paying 2% and he should be paying 2% its Canada, they have money and they should be paying 2%.
And I called him out on that and he wasnt happy about it and thats the way it is.
Im representing the US and he should be paying more than hes paying and he understands that.
I can imagine hes not that happy but thats the way it is.
At a final news conference, Trudeau played down the incident, saying he and Trump had enjoyed a great meeting.
He said his comment about Trump staffers jaws dropping was a reference to the announcement of the location of the next meeting of G7 leaders at the US presidential retreat, Camp David.
Last night, I made a reference to the fact there was an unscheduled press conference before my meeting with President Trump. I was happy to take part in it but it was certainly notable, Trudeau told reporters.
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.
Earlier, Johnson appeared perturbed at Trumps late arrival for a photocall.
An aide came out to tell the PM there was a delay. Johnson then asked how long it would take, and then gestured to the wall of cameras, saying: Were live now.
Half an hour? 45 minutes?
The aide left and then emerged a couple of minutes later
How are we doing? Johnson asked. Come on!
The aide scurried away. Johnson and Nato secretary general Jens Stoltenberg began rocking back and forth on their heels with their hands behind their backs.
Then, at 9.50am, POTUS emerged. Johnson gestured him toward Stoltenberg and the trio took a picture.
It is not the first time Trump and Trudeau have clashed.
The president branded his opposite number dishonest and weak at 2018s G7 summit in Canada, with the hosts accused of betraying their American neighbours with polarising statements on US trade policy.
The US president also accused Trudeau of making false statements during a press conference, and withdrew American support for the joint G7 communique.