User blog comment:Dave55811/"Coordinate" bets, anyone?/@comment-24.217.239.232-20140304022542/@comment-12642484-20140304040552

The only way for this to work would be if Grisha used to be the Beast Titan, then something happened that caused him to stop attacking mankind, then after the attack on Wall Maria his memories were reset (by someone with that Mysterious woman's abilities or by her herself) to the state it was before he stopped attacking mankind, This seems to be the only at least plausible possibility, however I still don't like it and IMO it is too much forced drama. The "betrayal by a close person" drama was already finished with Annie and Reiner and even if this is a bit different, the whole betrayal stories are starting to become boring, almost as if every single character we see in the story is a double agent...

So no: I doubt Isayama would go this route, it just does not seem to be the style of the manga and the only real "evidence" is the artstyle, which is known to be very inconsistent, for multiple reasons.