Amanda Seyfried surprises fans with impromptu performance at film premiere

Amanda Seyfried captivated the audience during the premiere of Testament of Ann Lee.

The Mean Girls actress unexpectedly took the stage and belted two songs from the film, Beautiful Treasure, a reimagined Shaker hymn, and Clothed by the Sun.

Following the screening of the film in New York City, the 40-year-old actress joined composer Daniel Blumberg for the performance.

Directed by Mona Fastvold, the historical drama sees Seyfried stepping into the shoes of Ann Lee, who was the English founder of American shakerism (United Society of Believers.

To begin their performance, the pair sat down at the piano to sing Beautiful Treasures.

Previously in conversation with Gold Derby, the Mama Mia! star shared, “I think one of the hardest things was the week in the studio where I did Beautiful Treasures, which is the montage where I lose all my babies.”

The pair then introduced one of the film's original songs, Clothed by the Sun.

“When I write songs, usually the best ones happen very quickly and naturally,” Blumberg said in a statement to Rolling Stone. “With Clothed by the Sun, I plugged in my electric guitar and it all came out in one piece.”

In addition to Seyfried, Thomasin Mckenzie, Lewis Pullman, Stacy Martin, Matthew Beard, Scott Handy, Viola Prettejohn, Jamie Bogyo, David Cale, Tim Blake Nelson and Christopher Abbott also star in the film.

The Testament of Ann Lee is slated for release on December 25.