Miller cut off contact with mother during We Need to Talk About Kevin shoot

Actor Ezra Miller cut off all contact with his mother while shooting harrowing drama We Need To Talk About Kevin because her loving nature crippled his ability to play a cold-blooded killer who murders his family.

In the film, Miller ends up in prison after committing a massacre at his high school and slaying his father and sister.

The movie follows his on-screen mom, played by Tilda Swinton, as she wonders whether her cold relationship with her son contributed to his eventual violence.

And Miller admits he had to ban communication with his real mother Marta in order to mimic his character's feelings.

He tells New York Magazine, "In the moments where my mind could escape Kevin's, I had this growing, gathering appreciation for everything that my mother did right. But to bring back to the forefront of my brain this loving, empathetic relationship with my mother would have been extremely detrimental to either me or the film, so it was really essential that she, uh, keep fair distance."

Marta only saw her son's work when the film premiered at the Cannes Film Festival in 2011 and she was rocked by the young actor's portrayal of a murderer.

Miller recalls, "I've never heard her cry like that. Like, audibly sobbing and shaking."