It was an unguarded misery-loves-company moment that went viral. It ended with U.S. President Donald Trump taking another personal shot at Prime Minister Justin Trudeau, calling him "two-faced."

Normally, royal receptions for visiting dignitaries at Buckingham Palace offer media outlets the video equivalent of wallpaper: boring, harmless. But Tuesday's reception turned into an international incident when video emerged of Trudeau at the reception apparently venting to French President Emmanuel Macron and U.K. Prime Minister Boris Johnson about Trump's unexpected marathon news media availability on Tuesday.

The fuss threatened to overshadow the military alliance's 70th anniversary celebrations in London and appears to have driven another personal wedge between Trudeau and the mercurial Trump.

Trudeau attempted to calm the political storm today, saying that he simply expressed surprise to Macron and Johnson at having to conduct a 30-minute press conference with Trump ahead of their bilateral meeting.

PM Justin Trudeau, France's Emmanuel Macron, UK PM Boris Johnson and other VIPs shared a few words at a Buckingham Palace reception Tuesday - and seemed to be talking about U.S. President Donald Trump's lengthy impromptu press conferences earlier in the day. 0:25

On the video, Johnson can be heard asking Macron, "Is that why you were late?"

"He was late because he takes a 40-minute press conference at the top," Trudeau is heard saying.

Trump is not mentioned by name in the exchange, but the video provided fodder for more behind-the-scenes and in-front-of-the-camera drama.

Trudeau said today that the U.S. president caught his own staff off-guard by saying the next G-7 summit will be hosted by the Americans at the presidential retreat at Camp David.

PM Justin Trudeau says that the comments that were overheard at a NATO reception weren't directly about President Donald Trump but rather about the unscheduled announcement about next years G7 meeting that will now be held at Camp David 2:12

"Every different leader has teams whose jaws drop at unscheduled surprises. Like that video itself, for example," he said.

Trudeau's attempt at a walkback did nothing to mollify Trump, who took a shot at the prime minister today before leaving the NATO summit early.

"He's two-faced," Trump said at a media availability with German Chancellor Angela Merkel. "I find him to be a nice guy, but the truth is, I called him out on the fact that he's not paying two per cent and I guess he's not very happy about it."

Trump appears to believe that Trudeau's quip was a response to an awkward moment during the two leaders' news conference the previous day, when he put the prime minister on the spot over whether Canada is meeting its defence spending commitments.

He jokingly called Canada "slightly delinquent" on meeting NATO's benchmark of spending the equivalent of two per cent of GDP on defence.

Trudeau said he's confident he still has a good working relationship with Trump.

An echo of the Charlevoix G-7

"I think people know that the relationship between Canada and the United States is deep and goes far beyond the relationship between the prime minister and the president, although I will say, as you all know, we have a very good and constructive relationship between me and the president," Trudeau said.

The personal sniping as the NATO meeting ended was an echo of Trump's public meltdown after the Charlevoix G7 in 2018, when the U.S. leader took offence at remarks Trudeau had made at that summit's closing news conference. Back then, Trudeau told journalists Canada would retaliate against U.S. tariffs on Canadian steel and aluminum products, calling the tariffs "kind of insulting."

Trump was barely in the air following the summit when he tweeted from Air Force One, accusing Trudeau of being "very dishonest and weak" and of making up "false statements."

The reaction from Trump this time was nowhere near as visceral, even though conservative news outlets in the U.S. have portrayed the incident as Trudeau and other world leaders laughing behind Trump's back.

As with last year's meltdown, the timing of this latest Trump eruption could have been better from a Canadian perspective. The spat blew up as the U.S., Mexico and Canada have been pushing for the final ratification of the new North American free trade deal — and after NATO allies had tried to present a united front and smooth over the divisions that marred the run-up to the summit.

A source in the Canadian government tells CBC News the Trudeau PMO is less concerned about this spat with the president than it was after the Charlevoix blowup, saying the trade talks are coming to a positive conclusion and the Canada-U.S. relationship is solid.

U.K. Prime Minister Boris Johnson said NATO is rock-solid in its commitment to protect its members, so the alliance should discuss emerging threats. 0:54

Prime Minister Johnson steered around the fallout from the dispute. He declared that the alliance is "rock solid" after seven decades and the moments of discord during the summit — including a tense public exchange between Trump and Macron over the Turkish incursion into Syria and the repatriation of ISIS fighters — were no more than family squabbles.

"There is far, far more that unites us than divides us," he said.

'Constructive ... productive'

NATO Secretary General Jen Stoltenberg downplayed the rifts and focused on the decisions made on Wednesday.

"Most of the time we agree and reach concrete conclusions. Sometimes we disagree," he said.

"And the meeting today was a meeting where there was a good atmosphere. It was very constructive and most importantly it was very productive."

NATO agreed to put more forces on high readiness under the "four-30s" plan — a U.S. initiative that requires the alliance to mobilize 30 troop battalions, 30 squadrons and 30 warships within 30 days of an emergency.

Canada's contribution to the readiness initiative will see the Liberal government add six fighter jets and a frigate to existing NATO deployments.

That brings the total Canadian commitment to 12 CF-18s, an expeditionary air task force, a C-140 maritime patrol aircraft, three frigates, a submarine, a mechanized infantry battalion, a mobile hospital and a platoon for chemical, biological, radiological and nuclear decontamination.

Trudeau promised the government would provide the necessary funds to ensure the units are trained and deployable on short notice.

Stolenberg also said NATO has declared that all 29 member countries would agree to use secure wireless telecommunications networks — a nod to American concerns about the Chinese tech giant Huawei and the security of the soon-to-be built 5G network service.

Canada has yet to decide whether it will ban Huawei from participating in building the system here.

Alliance delegates also talked about bringing China into the international arms control framework, pointing to the superpower-in-waiting's massive military expansion.

Scheer slams Trudeau's 'love of drama'

Back in Ottawa, Conservative Leader Andrew Scheer cited the NATO summit video in a speech to his caucus.

"At a time when Canada needs strong relationships more than ever, Justin Trudeau's poor judgment, lack of professionalism and love of drama continues to weaken Canada's position on the world stage," Scheer said, as assembled Tory MPs yelled, "Shame!"

NDP Leader Jagmeet Singh says the video showing the prime minister seemingly talking about Trump's behaviour to other world leaders at the NATO summit in London is typical Trudeau. Saying one thing in public and another in private. 0:52

NDP Leader Jagmeet Singh also seized on the moment, saying Trudeau has a record of saying one thing in public and something else behind closed doors.

"There's many reasons to criticize Mr. Trump, but criticizing about making someone late to a cocktail party is not one," he said.

David MacNaughton, Canada's former ambassador to the U.S., said the video gaffe must not be allowed to distract from efforts to get the trade deal ratified.

"The most important thing in the relationship is getting the USMCA passed," he told CBC, using the Americans' preferred title for the new North American free trade agreement. "And we shouldn't be distracted by this kind of stuff. We should get the deal done.

"The Mexicans know what they have to do to get this across the finish line, and they should just do it."

The deal has stalled in the U.S. Congress, where Democrats have been pushing for stricter enforcement measures on its labour and environmental standards. The American labour movement fears U.S. jobs will continue to head south if Mexico doesn't raise wages and bring in collective bargaining in a timely manner.

"What the Democrats have asked for in terms of enforceability, and what [U.S. Trade Representative Robert] Lighthizer has asked for in terms of enforceability, is what they're going to have to do to get this thing done," said MacNaughton.

"I know it's interesting, speculating ... and gossip and everything else, but it isn't actually enduring."