The Secret Circle revealed a wealth of information this week regarding the those ever-popular crystals. But that's nothing compared to the secret that will come out on April 19.

Indeed, when this CW drama returns from another hiatus, we'll finally learn the identity of John Blackwell's other offspring. Who do you think is related to Cassie? Let the theories fly as you watch the first official preview for the aptly-titled "Crystal."

The CW has also released its synopsis of this episode. Consider yourself warned: spoilers ahead...

To protect themselves from the witch hunters, Jake, Cassie and Faye seek out Jake’s grandfather Royce, to find his family’s crystal and are confronted with disturbing theories about the events of sixteen years ago. Meanwhile, Diana tries to balance her pursuit of the Glaser crystal with Melissa and Adam with her romantic life with Grant, who demands to know what she’s hiding.

At the same time, Callum attempts to re-insert himself into Melissa’s life. Charles and Jane plot their move against Blackwell.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.