It's a disgrace and I apologize to Justin Trudeau and there other people at G7.
The denunciation is less of a surprise when you consider that a month before Trump was elected, De Niro made a video in which he called him a "pig" and a "bullshit artist".
Trudeau has not issued any public remarks about Trump's latest attacks.
Trump's spate of Twitter tirades has seen a number of political leaders rally around Trudeau, including Conservative leader Andrew Scheer and incoming Ontario premier Doug Ford. Trump advisers also ripped Trudeau, branding him a back-stabber.
But Fox News host Brian Kilmeade had a different take, saying that De Niro's comments were yet another reason not to watch "Meet the Parents", a 2000 film in which De Niro co-starred.
'First, I wanna say, 'f**k Trump, ' the man started, causing many to cheer.
The gathered crowd seemed to agree with his message with applause, whoops and a standing ovation coming from the audience. It's "The Emperor's New Clothes" - the guy is a f***ing fool. our baby-in-chief - the "J******-in-chief" I call him,"De Niro said". This f***ing idiot is the President.
De Niro's new Toronto development will be built at 15 Mercer Street, near King Street West and Blue Jays Way, in the city's downtown core.
Ted Nugent tweeted: 'Damn shame Robert de Niro turned into such a hypocritical America hating drug-addled jerk'.
"America is being run by a madman who wouldn't recognize the truth if it came inside a bucket of his beloved Colonel Sanders Fried Chicken", De Niro said.