Attack On Titan season 2 brought a lot of surprises, and apparently we're still getting confirmation on some longstanding fan theories.
One of the latest secrets of Attack on Titan to come to light is the identity of one particular Titan that terrorized the Scout Regiment - but since this reveal is considered to be a MAJOR SPOILER for the Anime series, we'll leave the explanation down below, for anyone who wants to read.
Final Warning: Big Spoiler for Attack on Titan seasons 1 & 2 follows!
A Reddit thread picked up on some production artwork from the SNK Season 2 Festa, in which we see the Titan that Sasha fought in Episode 27 (Season 2 Episode 2) "Tadaima" or "I'm Home." As the notes on the artwork reportedly reveal, this Titan was Connie Springer's father.
Fans have been aware of Connie's parental connection to the Titans, as an immobilized Titan resembling his mother was seen seemingly welcoming him home to Ragako village. As season 2 ended, Connie personal tragedy helped Hange confirm a theory that the Titans are actually human beings in a transformed state.
As AoT fans in Reddit thread note, Attack on Titan creator Hajime Isayama actually intended for Connie best friend Sasha to die in the fight with the Mr. Springer Titan. Not only was Sasha intended to die, but apparently she would've died quite horribly, having her upper and lower jaws pried apart until her head ripped open.
Since both Sasha and Connie have become fan-favorites, Isayama spared Sasha from that gruesome death; spared Connie from having to find out his best friend was murdered by his father - who had been transformed into a monster. That would've been a harsh and very traumatic blow to fans - as would the apparent death that Isayama had planned for Connie, as well.