Amanda Seyfried wore unusual prosthetic for nude scenes in The Testament of Ann Lee

Amanda Seyfried has revealed she was wearing a "prosthetic butthole" during her intimate scenes in The Testament of Ann Lee.

In the period drama, the Mean Girls actress plays Ann Lee, an 18th-century English woman who turned to religion after losing four children and went on to found the Shakers movement.

For the nude sequences, such as the intimate childbirth scenes, Seyfried has revealed that she wore a "prosthetic butthole" to protect her modesty.

"This movie, it needed to be graphic, so, like, I had a prosthetic butthole," she said on BBC Radio 2's Scott Mills Breakfast Show.

When asked what the experience was like, Seyfried insisted it was "cool" and "exciting" and added, "I was pregnant and naked, but I wasn't naked at all."

The Oscar-nominated actress then noted that said body part does not actually appear in the movie.

"You cannot see my butthole in (the film), but I swear there is a prosthetic butthole there," she shared, to which presenter Mills asked why she needed to wear it if it wasn't going to be seen.

"Just in case," Seyfried replied, before quipping, "Gotta get people to the theatre."

The Mamma Mia! actress also pointed out that she wore a murkin - a pubic hair wig - while shooting her nude scene in the movie's final moments.

"At the end of the movie, I'm standing in front of a burning building with just a merkin. I felt so free," Seyfried praised.

The Testament of Ann Lee, which also stars Lewis Pullman, Thomasin McKenzie and Stacy Martin, will be released in U.K. cinemas on Friday.