Has anyone else noticed that the book only mentioned Two-bit having a sister once, the movie didn't mention her, and in the TV show, Two-bit's an only child? That leaves us with the question: what happened to her?

There's a few theories about what happened to her. (Please note that none of these are real theories. I'm just doing this for fun.)

The first is the most likely. That the producers simply forgot about it. I mean, the book was written in the 60s and the TV show was on around the 90s. Although, SE Hinton helped develop the show, I think. I doubt any author would forget that one of their characters is a sibling. 

Then there's the theory that the other Matthews sibling moved away. I'd say probably before the events in the book took place. "Kid sister" doesn't necisarily mean several years younger. It could mean a year, or even ten months. Regardless, she might've gone to live with a grandparent or something. 

Another theory is that she died at some point. 

The last one is just bat-crap crazy. 

If you watch the episode where Two-bit meets his dad, it suggests she never existed in the first place. Or Two-bit's dad didn't know about her because he's not her father.

That was fun. 

But seriously. What happened to Two-bit's sister?