'Pretty Little Liars' Author Sara Shepard Reveals Her Favorite 'A' Theories - 'It's Twins!'

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Seriously though... Who the heck is 'A'?!

WARNING: We're about to discuss some pretty little theories about who 'A' could be, but this is all just speculation! Sara Shepard does not know who 'A' is, and none of this is official.

Who the heck is 'A'?!

It's the question that has been haunting PLL fans for nearly six years, and now we're finally getting closer to the truth. From Mona's initial reign of text-message terror, to Shana's sneaky takeover, Pretty Little Liars has featured countless 'A' fake-outs and shake-ups, but the truly wicked one — 'Big A' — has yet to be revealed.

ETonline had an exclusive chat with one of the show's biggest fans, author Sara Shepard, who penned all 16 of the Pretty Little Liars books. We dug deep into Rosewood's twisted past to discuss her favorite theories including a hidden DiLaurentis twin and if one of the four liars has what it takes to be Big A!

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Right off the bat, Shepard was quick to tell ETonline that she honestly does not know who 'A' is. "I have not asked [executive producer Marlene King] who 'A' is," she confessed.

"I'm sure I could say, 'I really want to have a conversation, Marlene. I really want to know who 'A' is.' I'm sure I could, but I kind of want to just see what happens," she said. Shepard, who is guest-starring in an upcoming episode, added that it's "fun" for her to be out of the loop because then she can watch and live-tweet the show like a normal fan.

"I know that they know," Shepard teased. "I mean, I know as a writer they have to know, and they probably knew from very early on — if not the very beginning — how this was all going to end up, but like watching it like a fan."

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Speaking of fans, there are an endless amount of theories swirling around the interwebs trying to pinpoint the elusive PLL culprit. So what does Shepard think is the ultimate answer? "I am always saying in Twitter — it's twins!" she said with a laugh. "But I honestly don’t know."

"They do make a lot of references to identicals, and they do make a lot of references to twins, so I don’t know if that's just a red herring or not," she speculated. "It's also sort of fun if they are just playing because [the twin theory] is a reference to the books, and that's kind of a nod to the readers of the series."

Many fans who watch Pretty Little Liars have not delved into Shepard's epic 16-part book series, but they've heard enough to know that in the books Alison had a secret identical twin named Courtney DiLaurenits. Although Shepard does not think that King and the other PLL executive producers are hiding another identical Ali, she does think that something odd is going on in that DiLaurentis house.

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"I think these clues are there for a reason. Like the two dresses from the Christmas episode, for example, and Mrs. Dilaurentis keeping a secret for somebody," she said. "Who would you keep that secret for except somebody in your own family, or somebody very close to you? I don’t know if it's some sort of secret sibling or what."

Shepard added, "I do think it's going to be somebody that's close to the DiLaurentis family somehow." Dun dun duuuuun!

Of course there are plenty of fans out there who are pointing their fingers at our four liars — Hanna, Spencer, Emily and most of all, Aria. However, when we asked Shepard if she thinks 'Big A' could be one of our fierce foursome, her answer was short and to the point: "No, I don’t."

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"I don’t know what they're going to do, but I would never write that. You follow these girls around and you trust them and you love them," Shepard explained. "Everyone keeps saying Aria is 'A' and I'm like, 'Why?' I don't know why they're picking on Aria, but I know that as a writer you want to keep your beloved characters."

So what if Aria actually turned out to be 'Big A'? "I think that would be disappointing watching as a viewer," Shepard said. We couldn't agree more!

Don’t forget to join @ETnow as we live-tweet tonight's episode along with executive producer Marlene King and swoon-worthy star Keegan Allen!

Pretty Little Liars airs Tuesdays at 8 p.m. on ABC Family.

Which Pretty Little Liars theory is your favorite? Who do you think is 'Big A'? Shout out your thought on Twitter to @LeanneAguilera using the hashtag #ETnow.