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Kate and Leonardo have been best friends for 13 years, and she says their relationship helped their Revolutionary Road performances. "That was one of the great luxuries, the friendship that we have. We knew we have a trust that's so strong that we could push each other's buttons," she says. "Knowing each other as well as we do, we knew which buttons to push and when, and that was very, very valuable to us."

Leonardo is Skyping in to the Oprah Show studio from his Los Angeles home. He says his history with Kate, both onscreen and off, really influenced the final result of Revolutionary Road. "Kate and I have grown up in this industry together," he says. "We've been a support mechanism for each other for such a long period of time, and we've been there for each other and helped guide each other. It's amazing."

After Titanic, Leonardo says he and Kate had to be careful about shooting a second film together. "We knew that treading on any type of similar territory to Titanic would have been a mistake, so we fundamentally knew we'd have to try something different," he says. "We've always been in communication to find what that next great project was going to be."