Natalie Portman feels 'so lucky' to work with Reese Witherspoon on Lucy in the Sky

Natalie Portman felt "so lucky" to work with Reese Witherspoon on her new movie Lucy in the Sky.

The film, directed by Noah Hawley, follows the story of astronaut Lucy Cola, who begins to lose touch with reality and her sanity as she embarks on a devastating affair with a fellow officer after she returns to Earth following a long trip into space.

It was loosely based on the real-life activities of astronaut Lisa Nowak, who drove across the U.S. to try and kidnap the new girlfriend of her lover, William Oefelein.

Portman opened up about how she felt working with fellow Oscar winner Witherspoon, who produced and kickstarted the project.

"Reese was very involved, she helped develop the script so I am very grateful to her for helping create this character and working on details of it with Noah during the development... it was so lucky," she told Entertainment Tonight.

Witherspoon was originally set to star in the movie, alongside Jon Hamm and Dan Stevens, but eventually decided to step back and handed the leading lady reigns over the Portman instead.

"She's such a powerhouse," the Black Swan star gushed. "She's producing and making work for a lot of us, so I'm very grateful and it was really lucky to get to have a friend to get to call up and be like, 'What do you think about this? What's your take on this? Why did you choose this?' It was very lucky to have her insight."

Lucy in the Sky is released in cinemas on 4 October.