Seyfried said she too was doubtful when she was approached for a follow-up initially.
"Truthfully, when they were like, 'We're making Mamma Mia 2' I was like, 'That's going to be terrible.' But it's not! It's amazing," she told EW.
The film, titled "Mamma Mia!: Here We Go Again", will focus on Donna's (Meryl Streep) younger days. Actor Lily James plays the younger Donna in the movie.
"As soon as you see Lily on screen, you're like, 'Oh my God, that's Donna! I'm seeing Donna when she was wild and young and free, and she has the essence that Meryl brought to it. And it's kind of extraordinary," Seyfriend said.
"Everybody's back together and it's been 10 years. There's so much love and so much family that it's infused 100 times in this movie. It was so unexpected for me.
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