With the introduction of the Wicked Witch (guest star Rebecca Mader) coming soon on Once Upon a Time, there is speculation that she might be related to one of the characters.

TVLine reporter Matt Mitovich spoke in a "Spoiler Alert" video for the publication about how the Wicked Witch will relate to the other characters. Once co-creators Edward Kitsis and Adam Horowitz had perviously told TVLine that the Once Upon a Time family tree would be getting bigger this season.

Mitovich is speculating that the Wicked Witch will also be the sister of Regina (Lana Parrilla). This would make sense since Regina is also the villainous Evil Queen.

Mitovich is also reporting that the Wicked Witch is only going by the name of Wicked Witch for the ABC series. It is not yet known if she is the Wicked Witch of the West but she is not going by the name Elphaba, her name in the popular Broadway musical Wicked.

Once Upon a Time Spoilers: Peter Pan in Neverland Spinoff in the Works? 

The Wicked Witch will be the "big bad" for the second half of Once Upon a Time season 3. The characters will be traveling to Oz at some point in the second half of the season, though it is unknown if they will be staying there for multiple episodes as they did in the first half of the season with Neverland.

Once Upon a Time season 3 returns for its midseason premiere on Sunday, Mar. 9 at 8 p.m. on ABC.

Watch a trailer for the next episode of Once Upon a Time here: