During the season one finale of The CW's The Flash, Eddie Thawne killed himself to prevent one of his descendants, Eobard Thawne, aka Reverse Flash, from ever being born.

Of course, that sacrifice leads to the end of Reverse Flash — or so everyone thought. However, tonight's episode brings Eobard back from the dead (or from wherever those erased from existence go), possibly making Eddie's sacrifice last season mean nothing.

A new clip released from that episode shows the return of Reverse Flash, as the Flash recognizes him and wonders how he is actually alive. In his shock, Reverse Flash gets a good punch in and Barry quickly goes down: when he gets up, Reverse Flash is long gone.

It also seems that Reverse Flash still has a goal of killing the Flash and admits as much when he sees his old nemesis again.

So, how can Reverse Flash be alive? Well, it's obvious in the clip that this Reverse Flash is seeing Barry for the first time. Perhaps he's from a different Earth, because even if he were from the future or past, in theory, Eddie's sacrifice erased all versions of him from Earth-1's history. However, it seems that this Reverse Flash is from an earlier timeline, but if Eddie was one of his descendants, how is that possible? It's all very confusing, but fans will get answers tonight.

"What's interesting about it is this Thawne hasn't experienced last season yet, and Barry has," said executive producer Andrew Kreisberg to Entertainment Weekly. "On Barry's side, there's a lot stronger feelings — a lot more anger, a lot more betrayal, and in some cases, that's blinding Barry to what he needs to do. It's really an episode about Barry coming to terms with what he wants to do and what he should do regarding this version of Thawne. There are some great surprises and some character interactions between this Thawne and all of our characters. Again, they all have the benefit of having enjoyed last season and he hasn't."

So, not only does Team Flash still have to deal with Zoom, who easily out-matched Barry in their last fight, but now, they must face an old enemy who shouldn't exist as well.

The Flash airs on the CW on Tuesdays.