Britain's Princess Anne The Princess Royal, right, talks to NATO delegates from left, Canadian Prime Minister Justin Trudeau, Britain's Prime Minister Boris Johnson, French President Emmanuel Macron, during a reception at Buckingham Palace, in London, as Nato leaders attend to mark 70 years of the alliance, Tuesday Dec. 3, 2019.  While NATO leaders are publicly professing unity as they gather for the London summit, several seem to have been caught in an unguarded exchange on camera apparently gossiping about U.S. President Donald Trump’s behaviour. In footage recorded during the Buckingham Palace reception on Tuesday, Canadian Prime Minister Justin Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne. (Yui Mok/Pool via AP)

WATFORD, England (AP) — NATO leaders professed unity on Wednesday at a summit near London — but a spat over off-the-cuff chit chat at a royal reception rattled their show of solidarity.

U.S. President Donald Trump branded the leader of America’s northern neighbor “two-faced” after Canadian Prime Minister Justin Trudeau appeared to gossip about Trump in comments caught on camera and microphone.

Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne, daughter of Queen Elizabeth II at Tuesday evening’s Buckingham Palace reception for NATO leaders.

Trudeau could be heard saying incredulously, “he takes a 40-minute press conference off the top." Trudeau confirmed that was a reference to Trump’s long and unscheduled question-and-answer session with journalists earlier Tuesday.

Trudeau also said: “You just watched his team's jaws drop to the floor." He explained Wednesday that was in reference to Trump’s decision to hold the next Group of Seven meeting at Camp David, the presidential retreat.

Footage of the palace reception was recorded by a pool camera. The clip was posted online by Canadian broadcaster CBC and has been viewed more than 5 million times.

Speaking Wednesday at the summit venue in Watford, outside London, Trump said Trudeau was likely upset that the U.S. president had broached the fact that Canada falls short of the NATO target of spending 2% of its gross domestic product on defense.

“Well he's two-faced,” Trump told reporters. “And honestly, with Trudeau he's a nice guy, I find him to be a very nice guy but you know the truth is that I called him out on the fact that he's not paying 2% and I guess he's not very happy about it."

Trudeau had a quiet word and a handshake with Trump as he arrived at the summit Wednesday, and later tried to shrug off the episode.

“As you all know, we have a very good and constructive relationship between me and the president,” Trudeau told reporters at a news conference.

Asked if the incident had given him pause for thought, Trudeau said that ensuring the focus of attention remained on matters of substance “is something that we’re all going to try to do a little harder.”

Johnson, meanwhile, professed ignorance when asked by reporters about the conversation.

“That’s complete nonsense,” he said, adding: “I really don’t know what is being referred to there.”

Leaders of the 29 NATO states met to mark the 70th anniversary of the military alliance — and trying to patch up differences over defense spending, the alliance’s strategic direction and member nation Turkey’s military action in northern Syria.

The two-day gathering ended with a show of unity, as the leaders declared their commitment to the alliance’s principle of collective defense, saying in their final declaration that “an attack against one Ally shall be considered an attack against us all.”

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Rob Gillies in Toronto contributed to this report.

In this grab taken from video on Tuesday, Dec. 3, 2019, France's President Emmanuel Macro, centre right, gestures as he speaks during a NATO reception. While NATO leaders are professing unity as they gather for a summit near London, several seem to have been caught in an unguarded exchange on camera apparently gossiping about U.S. President Donald Trump’s behavior. In footage recorded during a reception at Buckingham Palace on Tuesday, Canadian Prime Minister Justin Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne. (Host Broadcaster via AP)
In this grab taken from video on Tuesday, Dec. 3, 2019, Britain's Prime Minister Boris Johnson, right, speaks during a NATO reception. While NATO leaders are professing unity as they gather for a summit near London, several seem to have been caught in an unguarded exchange on camera apparently gossiping about U.S. President Donald Trump’s behavior. In footage recorded during a reception at Buckingham Palace on Tuesday, Canadian Prime Minister Justin Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne. (Host Broadcaster via AP)
In this grab taken from video on Tuesday, Dec. 3, 2019, Canada's Prime Minister Justin Trudeau, centre, gestures as he speaks during a NATO reception. While NATO leaders are professing unity as they gather for a summit near London, several seem to have been caught in an unguarded exchange on camera apparently gossiping about U.S. President Donald Trump’s behavior. In footage recorded during a reception at Buckingham Palace on Tuesday, Canadian Prime Minister Justin Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne. (Host Broadcaster via AP)
U.S. President Donald Trump, left, and Canadian Prime Minister Justin Trudeau shake hands prior to a NATO round table meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. As NATO leaders meet and show that the world's biggest security alliance is adapting to modern threats, NATO Secretary-General Jens Stoltenberg is refusing to concede that the future of the 29-member alliance is under a cloud. (AP Photo/Frank Augstein)
U.S. President Donald Trump, center left, and Canadian Prime Minister Justin Trudeau arrive for a round table meeting during a NATO leaders meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. As NATO leaders meet and show that the world's biggest security alliance is adapting to modern threats, NATO Secretary-General Jens Stoltenberg is refusing to concede that the future of the 29-member alliance is under a cloud. (AP Photo/Evan Vucci)
NATO leaders from front left, Albanian Prime Minister Edi Rama, French President Emmanuel Macron, German Chancellor Angela Merkel, U.S. President Donald Trump and Turkish President Recep Tayyip Erdogan attend a ceremony event during a NATO leaders meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. NATO Secretary-General Jens Stoltenberg rejected Wednesday French criticism that the military alliance is suffering from brain death, and insisted that the organization is adapting to modern challenges. (AP Photo/Francisco Seco)
U.S. President Donald Trump, center, front, NATO Secretary General Jens Stoltenberg, center left, and Turkish President Recep Tayyip Erdogan, front right, pose with other NATO heads of state for a group photo during a NATO leaders meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. NATO Secretary-General Jens Stoltenberg rejected Wednesday French criticism that the military alliance is suffering from brain death, and insisted that the organization is adapting to modern challenges. (AP Photo/Francisco Seco)
Secreatary of State Mike Pompeo, center, smiles as he arrives to participate in a round table meeting during a NATO leaders meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. As NATO leaders meet and show that the world's biggest security alliance is adapting to modern threats, NATO Secretary-General Jens Stoltenberg is refusing to concede that the future of the 29-member alliance is under a cloud. (AP Photo/Evan Vucci)
U.S. President Donald Trump, left, and Canadian Prime Minister Justin Trudeau arrive for a round table meeting during a NATO leaders meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. As NATO leaders meet and show that the world's biggest security alliance is adapting to modern threats, NATO Secretary-General Jens Stoltenberg is refusing to concede that the future of the 29-member alliance is under a cloud. (AP Photo/Evan Vucci)
Canadian Prime Minister Justin Trudeau speaks during a media conference at the conclusion of a NATO leaders meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. NATO leaders papered over their differences Wednesday and vowed to respond as one to an attack on any of the 29 member countries, despite divisions over the priorities of the world's biggest security organization. (AP Photo/Frank Augstein)
Canadian Prime Minister Justin Trudeau speaks during a media conference at the conclusion of a NATO leaders meeting at The Grove hotel and resort in Watford, Hertfordshire, England, Wednesday, Dec. 4, 2019. NATO leaders papered over their differences Wednesday and vowed to respond as one to an attack on any of the 29 member countries, despite divisions over the priorities of the world's biggest security organization. (AP Photo/Frank Augstein)
Britain's Princess Anne The Princess Royal, right, talks to NATO delegates from left, Canadian Prime Minister Justin Trudeau and Britain's Prime Minister Boris Johnson, during a reception at Buckingham Palace, in London, as Nato leaders attend to mark 70 years of the alliance, Tuesday Dec. 3, 2019.  While NATO leaders are publicly professing unity as they gather for the London summit, several seem to have been caught in an unguarded exchange on camera apparently gossiping about U.S. President Donald Trump’s behaviour. In footage recorded during the Buckingham Palace reception on Tuesday, Canadian Prime Minister Justin Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne. (Yui Mok/Pool via AP)
Britain's Princess Anne The Princess Royal, left, talks to NATO delegates from left, Nato Secretary General Jens Stoltenberg, Canadian Prime Minister Justin Trudeau, French President Emmanuel Macron and Britain's Prime Minister Boris Johnson, during a reception at Buckingham Palace, in London, as Nato leaders attend to mark 70 years of the alliance, Tuesday Dec. 3, 2019.  While NATO leaders are publicly professing unity as they gather for the London summit, several seem to have been caught in an unguarded exchange on camera apparently gossiping about U.S. President Donald Trump’s behaviour. In footage recorded during the Buckingham Palace reception on Tuesday, Canadian Prime Minister Justin Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne. (Yui Mok/Pool via AP)
Britain's Princess Anne The Princess Royal talks to NATO delegates from left, Canadian Prime Minister Justin Trudeau, Britain's Prime Minister Boris Johnson, French President Emmanuel Macron and Nato Secretary General Jens Stoltenberg, obscured right, during a reception at Buckingham Palace, in London, as Nato leaders attend to mark 70 years of the alliance, Tuesday Dec. 3, 2019.  While NATO leaders are publicly professing unity as they gather for the London summit, several seem to have been caught in an unguarded exchange on camera apparently gossiping about U.S. President Donald Trump’s behaviour. In footage recorded during the Buckingham Palace reception on Tuesday, Canadian Prime Minister Justin Trudeau was seen standing in a huddle with French President Emmanuel Macron, British Prime Minister Boris Johnson, Dutch Prime Minister Mark Rutte and Britain’s Princess Anne. (Yui Mok/Pool via AP)