Jennifer Lawrence and David O. Russell make up perhaps one of today’s most famous director-actor duos. But that partnership almost didn’t happen.

Speaking at the Tribeca Film Festival Saturday night for its Directors Series, Russell revealed that Lawrence was the last person cast in both their first movie together, “Silver Linings Playbook,” and their second, “American Hustle.”

For “Silver Linings,” Russell said, “we thought you were too young and there were other actresses in the front of the line who were close to getting the role.” As for “American Hustle,” however, Lawrence was busy with other movies and “technically not available.”

“I called her up on her vacation and I said, ‘I feel like I would be remiss as your friend if I did not give you one last chance to say no to this role,” he recalled. “You said, ‘will I get to have big hair and long nails and be crazy?’ And I said yes, and you said, ‘Okay, I’ll do it.’”

The two went in-depth on their partnership, from when they first met (at an American Film Institute luncheon, which happened to be the same place she met another collaborator, Darren Aronofsky), the movies they’ve done and even teasing their future team-ups. Without revealing more details, Russell told Lawrence on stage, “I’m writing something for you now.”

Looking back to “Silver Linings Playbook,” Russell and Lawrence noted the actress’ youth — she turned 21 while shooting. “You shaped me,” she told the director.

“I would put it this way: She showed up and she was, like, a raw talent that had no neuroses and no self-consciousness,” he said. “She was completely fearless. She would come into the scene like a weather system and leave me and Bob [De Niro] and Bradley [Cooper] and Jacki Weaver and Chris Tucker just kind of like, wow.”

Tribeca Film Festival co-founder Robert De Niro would actually end up making a surprise appearance during the chat after Russell showed off a scene in “Silver Linings” in which Lawrence’s character confronted his. It’s one of the more dynamic scenes in the film, one of the four or five climaxes Russell said he likes his movies to have. But Lawrence hadn’t really prepared for it.

She admitted that she didn’t memorize her lines the night before. “There’s something about wrapping where I think I’m never going back to work again. I’m just like, ‘I’m gonna go home and watch TV!’” she said. “So I didn’t read my lines and it was that scene. I remember I went in and did it and then I couldn’t do it anymore after that.”

A moment Russell saw that wisdom in Lawrence, he remembered, was on the set of “Silver Linings,” and Lawrence had happened to be reading “Anna Karenina.” Russell (who clearly has not read the spoiler guidelines of the internet) spoiled the end, asking her, “Have you gotten to the part where she jumps in front of a train yet?”

Lawrence, she said, was “devastated.” Not just about the spoiler, of course, but of the fate of the classic’s protagonist.

“She started to cry. That’s how invested in that book you were,” he said. “You were so invested in the story of ‘Anna Karenina’ that you were emotionally devastated. You were not cynical about it and you were not ironic and you were not snarky. You were sincere. And as Miles Davis says, ‘all that matters is that you play with sincerity.’ And you were a tremendously sincere person, as well as being a very funny person.”

The two also touched on “American Hustle,” showing two scenes of the movie, including one which could have been very different. Lawrence’s character, Russell revealed, was originally supposed to hang herself.

However, he later decided that Lawrence’s character, Roslyn, couldn’t end her plot that way because “she’s too alive! She’s too much fun.” Instead, she had to decide to divorce Christian Bale’s character. “That was the only way to get rid of Roslyn,” Lawrence quipped.

Lawrence and Russell’s conversation came before another buzzed-about chat at the festival: De Niro with Martin Scorsese, which will take place Sunday afternoon.

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