"Such a great actor, what a big loss," Kidman said in a statement to E! News. "Sending love and prayers to James' family. He will be greatly missed."
Hemingway & Gellhorn tells the story of Ernest Hemingway and his journalist wife Martha Gellhorn. Owen played The Old Man and the Sea novelist with Kidman as Gellhorn. It was premiered a little over a year ago.
Directed by Philip Kaufman, the film went on to win two Emmys (out of 15 nominations!). Both Kidman and Owen were also nominated for Golden Globes and SAG Awards.
Gandolfini died Wednesday at age 51 after suffering a possible heart attack in Italy.