The footage, which was shot by the British host's pool camera, has since spread across the internet, with observers suggesting Trudeau and the other leaders were mocking Trump and wondering how the mercurial U.S. president will react.

NATO allies agreed to move toward spending 2 per cent of gross domestic product on defence by 2024.

Leaders from all 29 NATO member states are gathering in London this week to celebrate the 70th birthday of the alliance.

Prime Minister Justin Trudeau is expected to travel to London next month where recent comments by French President Emmanuel Macron questioning the viability of the alliance threaten to overshadow a celebration of NATO's 70th birthday.

Trudeau defended NATO after France's president suggested a lack of U.S. leadership is causing the 70-year-old military alliance's "brain death."

In case you missed the two-day summit, which German Chancellor Angela Merkel called "very intense," here are five key takeaways.

The Canadian military will command a new NATO training and capacity building mission in Iraq for its first year, Prime Minister Justin Trudeau announced in Brussels on Wednesday as part of the annual alliance summit.

Prime Minister Justin Trudeau said Tuesday that Canada is extending its NATO commitment in Latvia by another four years to March 2023 and will boost the number of troops in the country to 540 from the current 455 in a show of ongoing solidarity with the alliance.

The future of military alliances, the fight against climate change and even free trade are all expected to be on the agenda as Trump sits down with his NATO and G7 counterparts.