The tall, trim Trudeau, a liberal who beat incumbent conservative Stephen Harper last month, has inspired not just Twitter hashtags, but endless column inches (including here!) about his dashing good looks and windswept hair.
He's also the youngest leader at the Asia Pacific Economic Cooperation forum, six years the junior of Mexico's Enrique Peña Nieto, 49, who has also set some hearts aflutter. A local newspaper featured photos of them at the top of the front page and a story headlined, "Girls have only eyes for Trudeau, Nieto."
Obama, 54, who becomes the elder statesman among the three North American leaders, had his first bilateral meeting with Trudeau on Thursday. They discussed the fight against the Islamic State; Trudeau campaigned on a pledge to withdraw Canadian warplanes from the fight, but on Thursday he said his administration would continue other forms of aid.
Trudeau, whose father Pierre served as Canada's prime minister for a total of 15 years, showed off his bilingual skills, opening his remarks to reporters in French, before switching to English.
Obama praised his younger counterpart, citing the "incredible excitement" generated by his campaign and predicting the new prime minister would "provide a great boost of energy and transform the Canadian political landscape." Trudeau said he looked forward to visiting the White House, noting that his wife wanted tips from first lady Michelle Obama about the White House vegetable garden.
Trudeau's youthful rise to power has been compared to Obama's, and the American president couldn't resist jumping in when a reporter asked Trudeau whether he sought advice from Obama after taking office.
Obama said he told Trudeau: "Justin, congratulations, you and your family look great. I know Canadians are incredibly inspired by your message of hope and change. I just want to point out that I had no gray hair when I was in your shoes seven years ago. So if you don't want to have gray hair like me, you have to start dying it soon."
"So young, and yet so cynical," Trudeau interjected.
Trudeau later said the bigger lesson he internalized from his first phone call with Obama was about how fast his daughters have grown up since the American president was elected in 2008.
That "really struck home to me," said Trudeau, who has three children. "I am making sure to try and remain as attentive and present for my kids, not just because it makes me a better parent and a better person, but also because it's what keeps us focused as leaders on what actually matters."