Credit: ABC Family

Warning: This article contains major spoilers for the Pretty Little Liars Season 4 finale. Click away now if you don't want to know!

UPDATE 3/18: As we learned in the Season 4 finale, no, Spencer was not the one who attacked Ali. It turns out that she did kind of try to hit her with a shovel, but she ended up tripping. Ali found out about her pill habit, and Spencer went back to the barn and fell asleep. There was no way she was the one who attacked Ali. She also wasn't the one who attacked the girl in Ali's grave, at least according to Melissa, who apparently knows something. Whew.

Original article: 

We've known for a while that Spencer's brain is hiding a secret, and on Pretty Little Liars Season 4, Episode 21 (“She's Come Undone”), the show gave us our first concrete evidence of what that secret is: that she really did hurt Ali on the night she disappeared.

According to notes Spencer found at Ezra's, CeCe and Ms. DiLaurentis saw Spencer attack Ali with a shovel that night. CeCe was paid off not to tell, and Ali's mom presumably had her own motivations for keeping the secret. Spencer's parents helped with the cover up. 

There was a gap in Spencer's memory from that night, between her verbal fight with Ali and when she turned up back at the cabin. Obviously, reading that she'd attacked Ali freaked Spencer out. She's not sure of her own mind anymore. She tried to get her parents and Ms. DiLaurentis to admit it's true, but she didn't get a straight answer one way or the other. However, she did discover that she can get accidentally violent on pills, which lends credence to the idea that this secret is the real deal.

However, we're not convinced. Clearly, Spencer and Ali fought that night, and there are a lot of questions about what happened after, but we feel like there might be even more to the story. On Pretty Little Liars, there's always one more twist!

What do you think? Share your thoughts about tonight's episode in the comments below!

Rebecca Martin is an Associate Editor at Wetpaint Entertainment and our resident Game of Thrones, Breaking Bad, and genre TV expert. Follow her on Twitter and Google+!