Barbara Hershey, Rose McGowan (Photo: ABC/Jason Kempin/Getty Images)

What’s the root of evil? Another chapter in Storybrooke’s grim fairytale will be revealed with a look into the past of Cora, the evil queen’s even more evil mother, played by Barbara Hershey.

Rose McGowan (“Charmed”) has been cast to play a younger version of Cora on an upcoming episode of “Once Upon a Time,” according to Deadline.

She’ll guest star in one episode, appearing in a flashback that will explore the origins of the character and perhaps explain how Regina’s (Lana Parilla) mama got so mean.

Click here to catch-up on previous seasons episodes of “Once Upon a Time”

Watch Cora’s Arrival in Storybrooke in “Queen of Hearts”: