Natalie Portman turned down the role of an emotionally conflicted nun in new film Doubt because she didn’t “understand celibacy.”

Director John Patrick Shanley has revealed that the 27-year-old actress was once in the running for the part of Sister James, eventually taken by Amy Adams.

“We asked Natalie Portman, and Natalie was very interested but kept saying she had a problem,” Shanley explains.

“And we finally nailed down as to what the problem was. She basically said she didn’t understand celibacy.”

Doubt, which stars Oscar-winning entertainers Meryl Streep and Philip Seymour Hoffman, tells the story of a nun who confronts a priest after discovering he has been abusing a student.