Justin Trudeau, Emmanuel Macron and Boris Johnson have all been caught on a hot mic at the Buckingham Palace NATO reception Tuesday evening, appearing to gossip about Donald Trump and an impromptu lengthy press conference. 

In a clip being widely shared online the three world leaders seem to be discussing why the French President was late during the London summit, held to mark the alliance's 70th anniversary. Princess Anne also appears to be in the discussion but it is unclear if or how she responds.

None of the men mention Trump by name but Trudeau seems to be referring to the US president's lengthy talks with the media throughout Tuesday.    

British Prime Minister Johnson asks: 'Is that why you were late?'  Taking a swig of his drink Canadian Prime Minister Trudeau shoots back: 'He was late because he takes a 40 minute press conference off the top.'  

A timeline of the US president's day at the NATO summit shows Trump first met with Macron on Tuesday at 2pm GMT.  At 2:20pm the two opened their meeting to the press. By 3:30pm Trump held a bilateral meeting with Trudeau. 

The video being shared online then cuts to a later clip, which is without context, where Trudeau adds: 'You just watched his team's jaws drop to the floor.'  He then motions as if his jaw is dropping. It is not known if Trump is the focus of that comment as the video has been edited.  

The clip was first shared by the Canadian Broadcasting Corporation. 

Pictures from the event show the Princess Royal talking to Johnson and Trudeau. 

The world leaders were all in London Tuesday for a summit to mark the alliance's 70th anniversary. 

Trump was joined by first Lady Melania and the couple were pictured talking to the Queen and with Prince Charles and Camilla at the same event.  

POTUS had earlier needled Macron about accepting captured ISIS fighters – offering to 'give them to you' - during the  heated and lengthy joint news conference Trudeau appears to be referring to. 

Trump's Macron meeting was one of three bilateral sit-downs where he spoke and fielded questions from reporters for a total of two hours, flooding the media landscape on a week when House Democrats are proceeding with impeachment at home. 

The president earlier took a dig at Macron for France and other European nations being reluctant to accept nationals from their own countries who joined the fight alongside ISIS terrorists.

Trump turned to his counterpart and asked: 'Would you like some nice ISIS fighters? I could give them to you.' 

The moment came hours after Trump had blasted Macron for previous comments that NATO was suffering 'brain death'.  

Macron in an interview had said NATO was suffering 'brain death,' highlighted a split over Turkey, and said the treaty alliance must remained unified.

'You just can't go around making statements like that against NATO. It's very disrespectful,' Trump groused at the start of two days of meeting with world leaders, including Macron.

Trump called it a 'very, very nasty statement to essentially 28, including them, 28 countries' that are part of NATO. He spoke at his first bilateral meeting, with NATO Secretary General Jens Stoltenberg. 

'I heard that President Macron said that NATO was brain dead,' Trump said, in a long back-and-forth with reporters. 'I think that is very insulting towards a lot of different forces,' he added.

Trump rapped Macron for his words and ripped the French economy while also brandishing U.S. economic power in a growing trade spat with Paris.

'It's a tough statement though when you make a statement like that,' Trump complained.

'Nobody needs NATO more than France. You just look back over the long period of time,' Trump said. 'Frankly the one that benefits really the least is the United States.'

'We benefit the least. We’re helping Europe. Europe unites when they go against a common foe ... That may or may not be a foe,' Trump said, in a presumed reference to Russia.

Trump said of France: 'It's a very tough statement to make when you have such difficulty in France.

'They’ve had a very rough year,' and brought up the 'yellow vest' protests, said France had a high unemployment rate, and said it was 'not doing well economically.

He referenced new tariff escalations being recommended by U.S. trade representative Robert Lighthizer Monday. They include new tariffs on French champagne, wine, cheese, and other products totaling $2.4 billion.

'We're doing their wines and everything else,' Trump said. 'You just can't go around making statements like that against NATO. It's very disrespectful.'

By the evening, Trump offered the French president a ride in the 'Beast'. 

Trump also teed off on France's digital services tax which he said is unfair to U.S. tech giants like Facebook, Google, and Twitter.

'I'm not going to let people take advantage of American companies. Because if anybody's going to take advantage of American companies, it's going to be us,' Trump said. 

Trump made his remark about ISIS after pressing France to accept the return of more of its countrymen and women, and pledging they were currently being held under 'lock and key.'

'We have a tremendous amount of captured fighters, ISIS fighters over in Syria. And they are all under lock and key but many are from France, many from Germany and many are from the U.K. They’re mostly from Europe. And some of the countries are agreeing. I have not spoken to the president about that. Would you like some nice ISIS fighters? I can give them to you. You can take every one you want,' Trump quipped.

That drew a caution from Macron. 

'Let’s be serious,' the French leader scolded, before outlining his own position. 'It is true you have a current fighters coming from Europe. But it’s a minority problem of the overall problem we have. And I think the number one priority because it is not yet finished is to get rid of ISIS,' Macron lectured, as Trump listened to a translation of his remarks.

Trump has previously declared victory over ISIS, only to say a contingent of U.S. forces would remain.

'And it is not done, I'm sorry to say that,' Macron told him. 'Your number one problem are not the foreign fighters, it is the ISIS fighters in the region and you have more and more of these fighters due to the situation today,' he said.

The comment drew a counter from Trump. 'It's why he is a great politician. That was one of the greatest non-answers I've ever heard and that's okay,' Trump said.

'France has taken back some fighters, actually. We have a lot of fighters, he said, before noting that U.S. and allied forces captured '100 per cent of the caliphate.

During a separate meeting with Trudeau, Trump called Canada 'slightly delinquent,' even as he went after other nations for paying less than a 2 percent of GDP commitment on defense. 

He also singled out Germany, whose NATO contributions have hovered around 1 per cent. ''They would owe us money. You're talking about - really you're talking about trillions of dollars,' Trump said, bringing up compounded past years of sub-2 per cent spending. 

'Nobody has ever brought that up. They just keep talking about the present,' he said. 

It was after the reception with the Queen at Buckingham Palace, Trump offered Macron a ride in the Beast, his famous Cadillac equipped with armor, bullet-proof glass, and run-flat tires, en route to 10 Downing Street for a reception hosted by British Prime Minister Boris Johnson.

And it was there that Macron was pictured warmly clasping First Lady Melania Trump's hand. 

Macron made up for the chill in the air and in the day's earlier encounters with the warm handshake he gave to the first lady, who wore a yellow Valentino cape to the event. Trump was pictured looking on during the greeting.