'Once Upon A Time' season 6 spoilers: Victor Frankenstein returns; Belle's backstory to be told

Dr. Whale, also known as Frankenstein, the scientist from the Land Without Color, is returning to Storybrooke in an upcoming episode of "Once Upon A Time" season 6.

David Anders, who plays Dr. Whale/Frankenstein, is set to reprise his roles in a single sixth season 6 episode, Entertainment Weekly has learned. Dr. Whale was last seen in the previous installment when he delivered Zelena's (Rebecca Mader) baby after being forced into doing so by Emma Swan (Jennifer Morrison).

"If you're going to have Jekyll [Hank Harris] and Hyde [Sam Witwer], there has to be a mad scientist convention," "Once Upon A Time" executive producer Edward Kitsis told EW.

"Let's just say mad scientists stick together," executive producer Adam Horowitz added.

Anders, who also stars in The CW's "iZombie," is the latest "Once Upon A Time" actor to return to the series. It was previously announced that Jessy Schram, who plays Ashley Boyd/Cinderella, and Raphael Sbarge, who plays Dr. Hopper/Jiminy Cricket, will also be reprising their respective roles in the next installment.

Meanwhile, the upcoming season will reportedly delve deeper into Belle's (Emilie de Ravin) family and history. Fans might remember that Belle was last seen trapped in Pandora's box.

During the recently concluded San Diego Comic-Con, Horowitz said, "As soon as the premiere episode, we'll be digging into Belle's story."

"She won't be trapped for long," he added.

"She comes out of the box," de Ravin confirmed. "She's back in Storybrooke. And you learn a lot about Belle and her family in the process."

Belle's parents, Sir Maurice (Eric Keenleyside) and Colette (Frances O'Connor) have already been introduced in "Once Upon A Time." Maurice, the ruler of a kingdom, was still alive at the end of the fifth season. Colette, on the other hand, was killed during an ogre attack back in season 4.

It is unclear if Belle's backstory will focus on her relationship with her parents or if a long-lost sibling or another relative will be revealed.

The sixth season "Once Upon A Time" will premiere on Sunday, Sept. 25, at 8 p.m. EDT on ABC.