The Vampire Diaries: Nathalie Kelley teases Sybil's capacity for evil

Nathalie Kelley made sure she brushed up on her Greek mythology before auditioning for the role of Sybil, the mind-controlling siren and Big Bad for The Vampire Diaries‘ final season.

“I was really kind of a nerd growing up,” she tells EW. “I read a lot of Greek mythology as a child, so I really just brushed up on the stories.”

As Kelley sees it, Sybil “gets what she wants” — and her twisted mind will take her to new levels. “I think you’ll be surprised at her capacity for evil as the season develops,” says the actress.

Viewers learned in the trailer for Friday’s upcoming episode “An Eternity of Misery” that Sybil has a sister, but Kelley can’t say too much about her mysterious sibling. “I don’t want to give it away,” she says. “She’s an integral part of the story and Sybil’s backstory.”

In Friday’s episode, viewers will get a peek into Sybil’s origin story, and Kelley says a “more vulnerable, human side of her” will be on display. “She’s motivated sadly, by these tragic circumstances,” she says.

Apparently, Sybil has abandonment issues after facing a long-term exile. “When people are motivated by that,” Kelley warns, “they are capable of some pretty dark things.”

She also explains why Sybil is so determined to kill Bonnie. Last week, Sybil could not get over the fact that both Damon and Enzo cared for Bonnie so deeply. Kelley says it’s “what triggers her about Damon’s love for Elena and everyone’s love for Bonnie. She can’t fathom that love because she’s never had it.”

But don’t mistake Sybil’s affection for Damon for something deeper. “Damon can serve her,” Kelley says. Indeed, the siren is not interested in a romantic relationship. Instead, Sybil prefers “to be worshipped,” Kelley says. “She wants a loyal servant, and as long as Damon is a loyal servant to her, she appreciates him and knows his value.”

The Vampire Diaries airs Friday at 8 p.m. ET on The CW.