Cruel Summer is all about Kate and Jeanette, and which girl is telling the truth about Kate's time in captivity — but there's another person that fans can't help but obsess over. Who is Annabelle, the person that Kate claims she saw the day she was rescued from Martin's basement? Well, that's something the show is teasing out as slowly as possible — but it's not stopping fans from coming up with their own theories. The latest? What if Annabelle is, quite simply, Martin's sister?

Cruel Summer hasn't formally introduced us to anyone in Martin's family. We know his father died by suicide, and that for him, it's all about "picking your battles" when it comes to family — advice he gave Kate during their hunting trip in 1993. Yet Reddit user Intelligent-Path-459 noticed something intriguing in Episode 6, titled "An Ocean Inside Me."

In this episode, Jeanette sneaks into Martin's house yet again — and while that makes her look bad, she also witnesses Tanya, her friend Tennille's mother, getting drunk on Martin's couch. Tanya tells Martin (why, I have no idea, but she does) that her daughter's father isn't her biological dad, despite Tanya pumping him for child support every month. Jeanette uses this information to make sure Tanya never tells a soul that she was in the closet during her and Martin's hang out.

While this blackmail scheme is the overall point of the episode, there's a brief throwaway moment in which Tanya picks up a photo. Martin tells her that the person in the photo is his nephew. While he doesn't mention which sibling is his nephew's mother or father, it's worth considering that maybe, this nephew is his sister's child — a sister named Annabelle.