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Everyone in Rosewood has a secret — even those we trust most. When Pretty Little Liars returns this winter for Season 4B, we’ll find out Spencer has been hiding something from the Liars — something that happened the night Ali died.

Wetpaint Entertainment chatted with Troian Bellisario at a screening of the Pretty Little Liars Halloween episode at Hollywood Forever Cemetery in Los Angeles on Tuesday (October 15), and she told us all about Spencer’s “fun secret.” Unfortunately for Spoby fans, it’s going to have some serious consequences for Spencer and Toby’s relationship.

“You get to learn the most fun secret about Spencer, and that’s why wasn’t she with the rest of the girls when they woke up and why was she awake to hear Alison scream,” Troian told us. “As we’re going through the season you’re hearing a lot more and understanding more about the night and Spencer’s state and why she had the fight with Alison.”

Troian also teased a “very Patrick Bateman moment for Spencer” in the later episodes this season. “It definitely got messy.” Whoa. Does this mean we can expect Spencer to go American Psycho on “A”? There’s always a bed for you at Radley, Spencer.

Ultimately, Spencer’s secret will drive a wedge between her and Toby. After all, he doesn’t exactly trust her after she spilled the beans about the deal he made with “A” to the Liars. And with her co-star Keegan Allen currently in New York City for his stage debut, we’ve begun to question what makes Toby leave Rosewood.

“They definitely go through something really, really difficult which is this big secret that is revealed about Spencer and that comes between them,” Troian told us. “Spencer has to make a choice to be open and honest with him or to keep it a secret and maybe go even further down this dark path. It definitely drives a wedge between them.”

Yikes! We’re not looking forward to seeing Spencer come undone this season. Although, if a “Patrick Bateman moment” is in store for this pretty little liar, we know Troian is going to knock it out of the park. OK, so maybe now we’re a little excited to see how it all unfolds.

What do you think, Pretty Little Liars fans? Are you excited to see Spencer go semi-psycho again? Sound off in the comments!

Reporting by Lindsey Jordahl.

Catch the Pretty Little Liars Season 4 Halloween special on Tuesday, October 22, 2013 at 8 p.m. ET on ABC Family, followed by the series premiere of Ravenswood!

Crystal Bell is an editor at Wetpaint Entertainment and our resident fan-girl for all things Pretty Little Liars. Follow her on Twitter and Google+!

Credit: Celebified Photo: Pretty Little Liars Halloween Special "grave New World" Preview Photos: Ezra Lurks In The Shadows While The Girls Search For Ali!