“Pretty Little Liars” is my favorite show, well behind “Game of Thrones,” but I am admittedly obsessed with getting to the bottom of the “A” mystery and just so we are clear, my money is on Aria. Everything has been way too easy for Aria. To be fair: The Ezra reveal was a serious blow, but I think she was mainly upset because someone pulled the carpet out from under her. But alas, I am already going off topic, in addition to my belief that Aria will ultimately be revealed as “A.” I have an idea regarding my other favorite “Pretty Little Liar,” Spencer Hastings.

Many fans believed that Spencer was the killer responsible for the death of Ali. Even after Alison was revealed to be alive, fans believed that Spencer was responsible for the death of the girl in Ali’s grave. However, while nothing regarding the death of the girl in Ali’s grave has been revealed yet, Spencer’s name has been cleared by Alison. The series built up the possibility of Spencer being a killer for four seasons, and then, with one brief conversation with Ali, it was revealed that she is innocent. So what is Spencer’s big secret?

The Hastings have always tip-toed around Spencer, so has Mrs. DiLaurentis. She is also the only Liars to ever face off against Alison, so there has to be a missing “A”-related puzzle piece. I think Spencer’s big secret is that she is, in fact, a twin. Let’s face it: Rosewood is a town built upon lies and if there is a reigning family of Rosewood then it is the Hastings/DiLaurentis. So fans should prepare for many more shock and awe moments with this family.

The Spencer Hastings twin theory has been discussed before, with most of the theories relying on two very specific scenes in the Halloween episodes. In Season 2 episode 13 “The First Secret” Ali recites a story about two blonde twins who are fighting over a baby doll. In a shocking twist, one of the twins stabs the other in the heart, reportedly killing her and sending her to an asylum. Then in Season 3 episode 13 “This Is A Dark Ride” one of the twins from the story visits Hanna Marin on Halloween. It has never been confirmed if the twin is a ghost or actually alive, but one thing is for sure: Twins hold some significance in “Pretty Little Liars.” My thought is that Spencer has a twin, and the twin is also character fans know well -- Alison.

In a recent interview Sasha Pieterse revealed that Alison does not have a twin, and while this turns a bit of a wrench in this theory, the actress never mentioned anything about fraternal twins. And if you are a true fan of “Pretty Little Liars,” then you will know that this series is a stickler for details. So it’s still possible that Spencer and Alison could be fraternal twins. Here’s the theory. Spencer is admittedly the black sheep of the Hastings family. However maybe it’s not her erratic behavior that has caused such a rift. Maybe Alison and Spencer are fraternal twins who were separated at birth and spilt between the Hastings and DiLaurentis family.

It was previously revealed that Peter Hastings is the biological father of Jason DiLaurentis, so what’s one more illegitimate child? Melissa and Spencer have a strained relationship to say the least, but maybe the current secret she is harboring is not in regards to the girl in Ali’s grave, but instead about the connection between Spencer and Ali. In Season 4 episode 24 “A Is For Answers” Mr. Hastings reminds Mrs. DiLaurentis of their supposed agreement before the pair are questioned by Rosewood Police about their daughter’s whereabouts. Aside for his recent appearance in Season 5, Mr. DiLaurentis, Ali’s supposed father is literally never around, not in a flashback from when the Liars were younger, not for a memorial service, his character was barely even mentioned in dialogue. Maybe Mr. DiLaurentis couldn’t handle the “agreement” reached between his wife and the biological father of his children, so he deserted them.

More on Mr. Hastings: Why did he have so many photos of Alison in his desk? He attempted to qualm Spencer’s questions by claiming that the photos were for a private investigator. However, a P.I. would only need one or two, most certainly not a collection spanning years. The last piece of evidence that adds to this theory comes from the Season 4 Halloween episode “Grave New World” when Ali visits Spencer as she sleeps on her living room couch. The girls have a conversation about a variety of topics, starting with painkillers and moving to family. This episode premiered after Spencer’s discovery that Jason was her half-brother. Ali who is rummaging through Spencer’s bag states "You're really mad at me, aren't you? Not telling you about Jason." Still in shock, Spencer barely reacts, then Ali states that the relation “practically makes us sisters.” She continues and says "you deserve a decent sister." However Spencer has a sister and while Melissa is not winning Big Sister of Year awards, she is still her sister and pretty “decent” in my book. The way Ali said the quote, she seems to be implying that she herself -- as the sister, and fraternal twin of Spencer -- should be a better sister.

Check out the scene below and let us know what you think of this “Pretty Little Liars” theory! And don't forget to tune in to ABC Family tonight for an all new episode of "Pretty Little Liars"! Find out what to expect in tonight's episode "Surfing the Afershocks" here