"How I Live Now," a film that just premiered at Tiff starring Saoirse Ronan, may be about a third world war breaking out, but it's a love story at its heart. As a 19-year-old actress, Ronan is finding herself in more and more adult situations on screen, and "How I Live Now" was the actress' first experience filming a sex scene.

When MTV News' Josh Horowitz sat down with Ronan at Tiff, she recalled what it was like to go through a scene like that for the first time.

"I actually wasn't nervous about it," Ronan said. "It was always written in the script, and there needed to be a sex scene in this film. They needed to consummate their love, I think, in order for us to really feel the heartbreak when they're separated because obviously, it becomes a lot more intense after."

A lot of planning and discussion between Ronan and her director,...