Word is that Robbie Amell will be reprising his role as Ronnie Raymond, one half of the hero Firestorm. Amell, the cousin of Arrow's Stephen Amell, was part of the first season of the show but went missing and was presumed dead as season 2 kicked off. This was after a quick wedding with Caitlin Snow (Danielle Panabaker) who is going through some changes of her own adjusting to her Killer Frost powers. Exactly how Raymond will return is not known… but they evil doppelganger angle was already done and his character was killed… then again their was Flashpoint so who knows.
Raymond's return would be interesting not only for Team Flash and Caitlin, but also for Legends of Tomorrow as Martin Stein (Victor Garber) now joins with Jefferson Jackson (Franz Drameh) to form Firestorm. And in the comics, there is a third person in the Firestorm matrix, Jason Rusch and he and Ronnie join to make the hero as well.
I'm going with the idea that it's the Earth-1 Ronnie… it would have the biggest impact and we never saw a body.
The Flash returns Tuesday, Jan. 24th on The CW.