Evil Morty Backstory

Unless more is revealed we now kinda know evil mortys backstory. I will say I’m a little bit bummed he wasn’t connected out to Rick c-137 in anyway, or even prime Rick, but that’s fine he’s his own thing. I remember all the theory’s that he’s the one in the trailer or in the picture frame with Rick and what not, and while it is still possible, it seems unlikely to me. Any thoughts on his backstory?