Riverdale's Lili Reinhart Shoots Down A Common Fan Theory From "Body Double"

After last night's episode of The CW's Archie Comics adaptation Riverdale, in which Betty Cooper snapped and took revenge on Chuck Clayton after learning that Clayton's football teammates — including the recently-deceased Jason Blossom — had taken advantage of her sister Polly, Twitter lit up with a question: Does Polly Cooper really exist?

The idea is that, following Betty's mental break — in which she wore a wig and called herself Polly, among other things — there seemed to be a possibility that her not-yet-seen sister could in fact be a manifestation of Betty's psychosis, and not an actual, physical character who exists.

Happily, ComicBook.com was on the set of Riverdale last night and had the opportunity to speak with Lili Reinhart, who plays Betty, about this theory.

"I know tonight's episode may allude to that, but truly, it's just a moment of mental break, which I think everyone can relate to," Reinhart said. "She doesn't actually have a split personality, she's not actually schizophrenic, which is something that people have thought after seeing episode 3. She cares about her sister so much, and the fact that something so terrible happened to her sister causes her to kind of break down and go into defense mode. Betty has a lot of built-up anxiety and anger and frustration. Tonight's episode is kind of the boiling over point and that's why you see her alter ego. I would say it's more of an alter ego than a split personality. It's her bad side coming out."

Of course, fans who have been paying close attention to news surrounding the show will also know that Polly has been cast, and is to be played by actress Tiera Skovbye.

There's also the practical side of things: While it's plausible that some people might humor Betty, particularly her parents, who seem to want to control everything in her life and could see a delusion like that as a way to keep a handle on their daughter, it seems unlikely that people like Archie and Jughead — who have been Betty's friends all their lives and who would know for sure whether or not a sister existed — would go along with it. Cheryl Blossom, who knew Polly because of her relationship with Jason, could be the kind of person to keep the "secret" if she thought she could use it to twist the knife into Betty at some point, but she's so obsessed with learning the truth about Jason's killer that it seems like the duplicity would have come out last week, when Cheryl dropped her pretense of trying to befriend Betty and admitted she was just looking for information about Polly and Jason.

Betty's sister seems situated to play a bigger role later in the season, although it won't be for at least another week, as next week centers on Archie, Jughead, and the subplot with Miss Grundy.

Riverdale airs Thursday nights at 9 p.m. ET/PT on The CW.