Elle Fanning and Sarah Paulson are set to star in Mirrah Foulkes' I am Sybil, an upcoming film based on the famous case of Shirley Mason, who was given the alias Sybil to protect her identity. Mason's fascinating story first came into public view in 1973, when Flora Rheta Schreiber's non-fiction novel Sybil was published. The book quickly became a bestseller, with 6 million copies sold worldwide. According to the novel, Mason sought professional help for social anxiety and memory loss. Through treatment, the author shared, Mason's psychologist Connie Wilbur found that Mason had multiple personality disorder (now recognized as dissociative identity disorder) and manifested sixteen personalities due to sexual and physical abuse.

However, I Am Sybil will draw from a different book about Mason's ordeal for its plot, Sybil Exposed: The Extraordinary Story Behind the Famous Multiple Personality Case. The 2011 book by Debbie Nathan argued the authenticity of the 1973 bestseller, with the author claiming much of the 1973 novel was based on a lie.

I Am Sybil is not the first film to explore the well-known case. Sally Field starred as the titular character, with Joanne Woodward as the psychiatrist, in the 1976 CBS made-for-television film Sybil. The film gained critical praise and four Emmy Awards, including the best actress win for Field. In 2007, a second made-for-television adaptation (also titled Sybil), starring Tammy Blanchard and Jessica Lange, aired on CBS. While the second film's reception was less favorable than the first, Blanchard and Lange were praised for their portrayals.

Related: The Best Movies and TV Shows That Put a Spotlight on Mental Health

Who Will Portray Sybil?

Elle Fanning in The Girl from Plainville
NBCUniversal Global Distribution

What roles Fanning and Paulson have been cast in remains unconfirmed, but Deadline, who first reported the news, says sources have Fanning as Mason, with Paulson as Wilbur. I Am Sybil is directed by Foulkes from a script co-written with Jen Silverman. Jennifer Todd for Jennifer Todd Pictures, Annapurna, and Ellen Goldsmith-Vein and Lindsay Williams for The Gotham Group serve as producers.

Fanning is an Emmy and Golden Globe-nominated actress who currently stars in the third season of Hulu's The Great as Catherine the Great. She has several upcoming projects in the works, including roles in Karim Aïnouz's Rosebushpruning and the Bob Dylan biopic A Complete Unknown. She will play the role of Ali MacGraw in the upcoming film Francis and the Godfather, which tells the story of a young Francis Ford Coppola facing off against The Godfather producer Robert Evans during the film's production. Fanning will also appear in The Nightingale, opposite sister Dakota Fanning.

Paulson is an Emmy Award and Golden Globe winner. She is a recurring collaborator of Ryan Murphy's and has appeared in a number of his series, including multiple seasons of American Horror Story, Ratched, Impeachment: American Crime Story, and The People v. O. J. Simpson (which earned the actress an Emmy Award). Paulson will next appear in the horror thriller Dust, and as the infamous Gwen Shamblin in a scripted series based on HBO's docuseries The Way Down: God, Greed, and the Cult of Gwen Shamblin.