Cooper landed the role of De Niro's son Pat in the film, and for a brief moment the senior actor even entertained the idea of having the 37-year-old's mom, Gloria, join the project to complete their family, reported Femalefirst.
De Niro, 69, spoke to director David O Russell about his casting ideas, even though Gloria had never acted before, and thought she would be perfect because the Coopers hail from Philadelphia, Pennsylvania, the same town as the movie family.
Cooper admits he began to worry that his co-star was serious about bringing his mother onboard until producers found actress Jacki Weaver as the perfect replacement.
Recalling the moment De Niro proposed the plan, 'The Hangover' star said, "I was like, 'What?' (De Niro said) 'I'll talk to Dave, maybe your mom should play your mom'. And he literally called Dave and said, 'Maybe Mrs Cooper plays my wife'. And we were gonna screen test my mom to play (Dolores) and then Jacki (came along)..".
Gloria stuck around the set to offer Weaver tips on how to portray a typical Philadelphia matriarch and the two women grew so close, the 'Animal Kingdom' actress actually began to act like Cooper's own mom would.
"Jacki spent so much time with my mom and Jacki's the same height as my mother, so she kinda, like, plays my mom in the movie. I don't know what he (De Niro) was talking about (casting Gloria), I literally don't know what he was thinking," said Cooper.