Two sisters learn their long-lost mother is a famous soap opera star in the Sundance darling Before You Know It -- and ET is exclusively debuting the trailer.

Before You Know It follows Rachel Gurner (Hannah Pearl Utt), who still lives in her childhood home with her actress sister, Jackie (Jen Tullock) and their eccentric playwright father (Mandy Patinkin). But their day-to-day dysfunction gets even more dramatic when the sisters find out their presumed-deceased mother is not only alive but thriving as a daytime soap actress.

Judith Light -- who herself starred on a soap, One Life to Live, from 1977 to '83 -- plays Sherrell Gearhardt, whose character on the long-running Time Will Tell is in jeopardy of being written out. When Rachel and Jackie visit the set and confront their mother, the entire family must try to come of age.

"She was so sweet, though," Jackie says of meeting Sherrell.

"No, Jackie. She abandoned her children," Rachel replies.

The movie also stars Mike Colter (Marvel's Luke Cage) as the family's put-upon accountant, Oona Yaffe as Jackie's 13-year-old daughter and Alec Baldwin as a child therapist.

Before You Know It was written by Utt and Tullock and directed by the former. It had its premiere at the Sundance Film Festival, screened as the closing night film of Outfest 2019 and opens in theaters on Aug. 30. Watch the trailer above and see the movie's poster below.

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