The Season 2 finale of The Flash saw Barry go back in time to save his mother which will impact Season 3 as the timeline has been altered.
The title of the first episode of Season 3 is "Flashpoint," which fans will recognize as the similar DC Comics storyline.
"People were like, 'Why did he do that?' And I think that he wasn't going to do that, but I think that sitting on that porch, having just defeated Zoom, Iris says to Barry what he's always wanted to hear, and he feels empty inside," explained Gustin. "That was the moment... As selfish as it was that Barry wanted his parents, I think it's more about 'these two speedsters took away their life because of me and they deserve to have a chance at life. I can't do this, I need to give them that chance.'"
Supergirl has also come over to The CW for its Season 2, and Kevin Smith asked The Flash cast if any of the first few Season 3 scripts have mentioned Kara Danvers. Gustin says the scripts haven't and offers The Flash Season 3 isn't totally about Flashpoint (note: The CW announced a mega DC TV crossover which will feature Supergirl).
"Not yet," Gustin responded when asked if a Supergirl storyline was involved in the first few Flash Season 3 scripts. "It's pretty Flashpoint focused right now, which I think we are going to see the repercussions coming out of Flashpoint. There will be ramifications all season long from Flashpoint."
Smith then asks if it's an all-season Flashpoint.
"I think we can state Flashpoint does not last all season long," Gustin said. "But there are permanent ramifications."
"The Flash" Season 3 premiers Tuesday, October 4th also starring Jesse L. Martin, Tom Cavanagh, Candice Patton, Danielle Panabaker, Carlos Valdes, Keiynan Lonsdale and Tom Felton.
Watch The Flash Season 3 Comic-Con trailer: