The verbal attack came following what Trump described as Trudeau's "false statements" on trade relations during the closing G7 news conference.
"Mr. De Niro's comments were unscripted and unexpected".
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In two tweets that announced the end of US support for the joint G-7 statement, Trump claimed Trudeau made "false statements" during a prior news conference and went on to lambaste the Canadian leader. Trump called Trudeau "dishonest" and "weak" following the summit on Saturday. Trump advisers also ripped Trudeau, branding him a back-stabber.
He suggested the comments were insensitive to the fact that Trump was trying to look strong on his way to an important summit with North Korea and said there is a "special place in hell" for people like Trudeau.
This isn't the first time De Niro has gone after Trump.
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De Niro's negative opinions about Trump are nothing new. During the opening lunch at the Tribeca Film Festival in April, the actor called Trump a "mad man" and a "low life".
"Bruce, you can rock the house like nobody else", said De Niro.
The CBS television network, which was broadcasting the event live but with a delay of a few seconds, scrambled to bleep out De Niro's expletive.
Trump Responds To Robert De Niro, Calls Him 'Punch-Drunk'
Ahead of the 2016 presidential election, De Niro said he'd like to "punch [Trump] in the face". In January of this year, the actor called Trump a "f**king idiot" in a profanity-laced rant .