"It's kind of the origin of Mirror Master...We're really excited," said Aaron. Added Todd, "It's the origin story of him, but it's this struggle between Mirror Master and Captain Cold and you get to see who comes out on top."

You'll have to wait until the fall to find out who that is—but you should know that everyone on The Flash was very excited for Miller's return. "We're excited to have Wentworth back because he always brings this amazing presence," said Aaron. Miller is the first DC TV actor to strike a unique deal that allows him to be a series regular on every CW superhero show: Flash, Arrow, Legends of Tomorrow and now Supergirl.

Rickards starred on Awkward for five seasons after a memorable turn on One Tree Hill. She also appeared in two episodes of American Horror Story's first season.

The Flash season three premieres Tuesday, Oct. 4 at 8 p.m. on The CW.