"I'm gonna say one thing. '**** Trump'," he said, which garnered him a sustained standing ovation from the crowd.
As it was live TV on a delay his speech had to be bleeped.
Reacting, Mr Graham criticised De Niro for cursing the president while he was "making history" through talks with North Korea.
"Those in the audience should have walked out on such a blatant display of disrespect," he said. "But instead, he gets a standing ovation."
"The unbridled hate many in Hollywood have for this president is unreal. There is a battle being waged for direction and the future of this nation-a battle between good and evil-and we need to pray.
Franklin Graham has been a vocal supporter of Trump since he's taken office.
Speaking to Premier earlier in the year, he claimed that God had made him leader of the country.
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