Well, this is unexpected! As you can see below, Rick Cosnett has confirmed that he's coming back to The Flash, but who will he be playing? In most shows, it would be logical to assume that he'll just reprise the role of Eddie Thawne in a flashback, but in this series, there are a number of possibilities.
It could be that we're going to meet an alternate Earth version of Eddie or that some sort of time travel shenanigans will be involved, but it's hard to tell from this Tweet whether it's a one-off appearance or something more permanent. For some time, though, fans have wanted to see Eddie back in The Flash.
Could it be that Eddie is actually Savitar? His body was pulled into that portal in the season one finale...