Recreating one of history’s darkest days was not an easy feat for Natalie Portman.

The actress says that she had to tap into her darkest emotions to portray Jacqueline Kennedy Onassis during former President John F. Kennedy‘s 1963 assassination for the upcoming drama Jackie.

“The most difficult scene was definitely the assassination scene,” Portman said at the PEOPLE / EW / InStyle studio at the Toronto International Film Festival. “To try and capture that most awful of emotions and the suddenness of that emotion, in the midst of quite a technical shoot – because we were recreating shots that really existed.”

Portman, 35, said that hearing stories of the Dallas assassination from her own relatives helped her understand the trauma.

Jackie, which premiered at TIFF on Sunday night, follows Kennedy Onassis after her husband’s death.

Beyond experimenting with what Kennedy Onassis might have felt, Portman said she also, “of course,” focused on recreating “the physical appearance of the character, the clothes, the hair and makeup, the details of how she spoke and learning the accent and the rhythms and the voice.”

Most crucial, though, Portman stressed, was the “emotional and spiritual” aspects of the late fashion icon, who shared two children – John Jr. and Caroline – with President Kennedy.

Portman’s hard work – and imagination – are now paying off. Her turn as Kennedy Onassis is earning her rave reviews and early Oscar buzz.

Jackie, which costars Peter Sarsgaard and Greta Gerwig, is set for a 2017 premiere.

  • Stage