The Reverse-Flash who will appear later this year on The Flash is not, as many fans had predicted, from Earth-2, showrunner Andrew Kreisberg told EW's spoiler column.
Instead, the character apparently comes from "an earlier timeline," and is the same Reverse-Flash we knew from last year.
“Time on our show does not unfold linearly,” Kreisberg said. “Sometimes you’ve seen events from one direction and then you start to see them from the other. This Reverse-Flash is not exactly the Reverse-Flash that we saw disintegrate at the end of the year. It’s a Reverse-Flash from an earlier timeline. It’s not the Earth-Two Reverse-Flash, it’s the Reverse-Flash. That is, hands down, one of our best episodes.”
It seems likely, given that explanation, that bit of context, that this is the Reverse-Flash who killed Vibe before Barry Allen reset the timeline in the Season One episode "Out of Time."
The Flash returns on Tuesday at 8 p.m. ET/PT on The CW with a new episode, titled "Potential Energy."
In that episode, The Flash is torn between revealing his identity to Patty and keeping his secret to protect to her.