Isabelle Huppert stayed in character while filming 'Greta,' scared wits out of Chloe Gracë Moretz

She said it was "really intense at times."

If you're going to play a controlling, terrifying character, you may as well go all in.

That's why Isabelle Huppert chose to stay in character during the filing of the new thriller "Greta." Huppert and co-star Chloë Grace Moretz stopped by the ABC News studios to promote the movie.

"I think it was really difficult for Chloë sometimes," Huppert said in an appearance on "Popcorn with Peter Travers." "I really was giving her a hard time. And myself, the most horrible things I was doing, the more pleasurable it was for me. But it was also due to [director] Neil Jordan's vision and staging. The movie, as horrible as it is, it's also a lot of fun because there was such a great sense of humor in it all the time. And it adds to the off balance and mystery to the female."

Huppert plays a woman, Greta, with awful secrets. She appears to be an unassuming piano teacher, but there’s something much more dark and sinister in the works.

This is first film for Huppert and Moretz as a co-starring team, and if you like thrillers, get ready for the good stuff.

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Moretz said, "It was wonderful experience building our relationship on screen. And obviously of course off screen. We had such a nice time building that love relationship in the beginning. And then to watch it decay and fall apart, and the psychosis take over, it was really fun to shoot. But also, it was difficult and really intense at times."

"Greta" hits theaters everywhere on Friday.