French director Fabienne Berthaud brings her third feature film, "Sky," to the Toronto International Film Festival, and like each of her previous entries it stars her favorite collaborator, Diane Kruger. We sat down to speak to Berthaud and Kruger about that relationship and what's next now that this project is finished — well, almost finished: Though she says she completed work on the film five days before its debut, Berthaud still has not finished adding the closing credits.

This is your third film together. How has this collaborative relationship developed?
FABIENNE BERTHAUD: It was really hard to collaborate with her. (laughs) No, I think it's easier and easier each movie we do together because the more we know each other, the more we can go into deep things. In fact, why I want to work with Diane — of course, I love her and she is an inspiration for me — but it is also interesting to work with the same person. I can say, 'I want to now take her into this universe, in a love story, in a violent moment. You know what? To explore more and more and more.' I like this. I like when she's a little bit in danger.

DIANE KRUGER: It's really great to get to work with the same person over and over again. I feel like we've grown together. It was her first film and my first film when we first started working, and we've created this little family for ourselves. It's so amazing to how much she's matured and how much she's become the general on set, really. We never had money for the first movie, it was so crazy. And now we've made a film in the U.S., and for me as an actress, I would do anything for her because I trust her 100 percent. She could literally ask anything of me.

FB: This is why I like working with her, because she always says yes.

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The structure of the story is very lyrical and flowing. How would you describe your writing style?
FB: The problem is I can't explain how I'm working. Because I'm not intellectual at all, and I always feel emotion. If I wake up one day and I am on a scene and suddenly I say, 'OK, what is she doing now?' I write, and I can say, 'No, she will go there.'

DK: The script for her is more of a blueprint. She has the story, and a lot of it organically evolves when we're shooting.

Ms. Kruger, what for you is the key to creating this type of quiet, internal performance?
DK: It's the situation. She shoots very much in a documentary style, meaning she frames herself and she's sort of with us, so the scenes never really feel like they're scenes. It feels like we're in a moment. And sometimes I don't need to say anything, I don't need to say what is written because the situation is self-explanatory. I really felt these. I've been on this journey creating this character for four years with Fabienne. By the time we started shooting, I was Romy. I knew exactly where she was coming from, where she was going. So I was trying to basically just be real at the moment.

FB: At the moment, at the right moment, at the good place. That's it. In fact, it's easy when you are with good people in the right location at the right moment.

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You're also a novelist, Ms. Berthaud. What kind of impact does that have on your filmmaking?
FB: I think I am doing exactly the same, but I change my tool. That's it. My camera is like my pencil when I work. It's why I need to use a camera I can hold myself. I write with my camera. It's always a work in progress. When we make movies is when we are with people and all of them have talent and we share talents on the same project. When you are a novelist, you are alone. But it's great, too. I love that.

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And do you already have your next collaboration in mind?
DK: I'm putting a lot of pressure on her. She told me an idea about a year ago, just before we started filming, and my heart just went, 'Ah, we have to make this, and can you please not wait four years?' I can't wait. I want her to be writing right now.

FB: But first I have to finish the end credits of this one. (laughs)

Follow Ned Ehrbar on Twitter: @nedrick