The Taxi Driver actor was chatting to host Katie Couric about how director David O. Russell's bipolar son Matthew inspired the story of Pat Solitano, a teacher who also suffers from the condition and is played by Bradley Cooper in the film.
When Couric asked if it was a ""great responsibility"" working on a movie so important to the filmmaker, De Niro, who plays Cooper's onscreen father, became teary-eyed.
He told the presenter, ""Of course, I, um - I understand. I don't like to get emotional, but I know exactly what he goes through.""
Both De Niro and Cooper are up for Oscars at the Academy Awards prizegiving later this month (Feb13).