The verbal attack came following what Trump described as Trudeau's "false statements" on trade relations during the closing G7 news conference.
While it was hoped that the trip could be used to help defuse tensions over a brewing trade war between the two countries, Trump began firing off tweets lashing out at Trudeau nearly as soon as he left.
"F*** Trump!" he exclaimed. "It's a disgrace and I apologize to Justin Trudeau and the other people at the G-7".
Trump responded on Twitter by slamming Trudeau as "very dishonest and weak".
"De Niro represents exactly what's going on in this country", he said. "And that's what bad-faith Justin Trudeau did with that stunt news conference".
Robert DeNiro got right to the point when he took the stage in NY to present a Tony Award on Sunday night, but the television audience didn't get to hear it.
Toronto Mayor John Tory, speaking moments later, addressed De Niro's remarks, saying only: "Thank you".
However, the audience inside the venue could hear every word of De Niro's rant. In addition to appearing many times as Special Counsel Robert Mueller on "Saturday Night Live", he publicly called Trump and "idiot" who "lacks any sense of humanity or compassion" in March.
"Bruce, you can rock the house like nobody else", he said.
The expletive, known as the F-bomb, was bleeped by the CBS network for millions of television watchers at home, a CBS spokeswoman said. The play also provided one of the best comedic bits for the evening, with the joke that the play's titular angel would chase winners offstage in lieu of being played off.
'Wake up Punchy!' Trump hits back at Robert De Niro
Trump was on his way to Singapore to meet with North Korean leader Kim Jong-un as the Broadway awards show was taking place. Granted, we don't want that remark to sound too disparaging towards De Niro because we all know that he's an acting icon.