Michael Sheen Replaces Paul Bettany in Showtime's ‘Masters of Sex’

“Twilight Saga” star Sheen will play sex researcher William Masters; Lizzy Caplan will play his partner

Michael Sheen is stepping into Paul Bettany's sex-researcher shoes.

The "Twilight Saga" and "Frost/Nixon" actor has been cast in the title role of Showtime's upcoming pilot "Masters of Sex." Sheen is replacing "A Beautiful Mind" star Bettany, who withdrew from the project in January for undisclosed reasons.

Sheen will play William Masters, who together with Virginia Johnson pioneered the field of sex research in the 1960s. The actor will also serve as a producer on the project.

Also read: Paul Bettany Pulls Out of Showtime's "Masters of Sex" Pilot

Lizzy Caplan ("Mean Girls," "Cloverfield") will play Johnson, Showtime also said Thursday.

Production on the Sony Pictures Television pilot will begin in New York in March. Michelle Ashford, Judith Verno, Sarah Timberman and Carl Beverly are executive-producing.

The project is based on the Thomas Maier book "Masters of Sex: The Life and Times of William Masters and Virginia Johnson, the Couple Who Taught America How to Love." Ashford, Timberman and Beverly penned the script.