De Niro is a highly respected actor, having garnered two Oscars for his roles in Raging Bull and The Godfather: Part II.
After the applause subsided, De Niro reiterated his apology, this time focusing on Canada's Prime Minister Justin Trudeau and "the other people" at the Group of Seven summit which took place last weekend.
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.
Although De Niro was heavily censored during the US telecast, his comments weren't bleeped during the Australian telecast.
"F*** Trump!" he exclaimed.
Trump took to Twitter to blast Trudeau, calling him "very dishonest and weak" shortly after leaving the summit early aboard Air Force One. Trump advisers also ripped Trudeau, branding him a back-stabber.
Trudeau said Canada "will not be pushed around".
When asked about De Niro's remarks, Seawright said he probably would have chosen different words but seemed to praise De Niro for voicing people's "frustration".
A month later during the opening night of the 2018 Tribeca Film Festival, De Niro referred to Trump as the "lowlife-in-chief", HuffPost reported.
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.