ENTERTAINMENT NEWS - The 71-year-old Oscar winner wrote on Twitter: "Well... I'm in Momma Mia 2." It's not known what role she will play.
The singer is currently in the UK, where filming is taking place for the follow-up to the Abba musical, set for release next summer.
Many of the characters from the original film, including Meryl Streep, Pierce Brosnan and Dame Julie Walters, will also appear in the sequel.
Cher would not be drawn on the name of her character or what songs she would be singing, but did tweet song title Fernando - followed by a thinking emoji.
Cher also confirmed she had been rehearsing dance routines, tweeting: "Just went through two dance numbers, everyone's great."
It will be the singer's first appearance in a film since 2010.