We saw how at the end of the season 2 Flash went back in time and saved his mother from the Reverse Flash, as a result, changed the timeline. In DC comics, due to change in the timeline, Barry never becomes the Flash, Justice League is fractured and superheroes start fighting amongst themselves, and as a result, Earth is destroyed.
Grant Gustin revealed the title of the first episode of season 3 on his twitter handle – “Flashpoint”. He wrote “We are definitely doing this FP thing our own way. I have read Flashpoint, I have seen the amazing animated film. This will be its own thing.”
He said “Barry’s memories are starting to get replaced from the previous timeline with new memories, but when he feels that it’s happening, he realizes how selfish a decision he took. Team Flash doesn’t exist anymore, Cisco is a billionaire”.
At the MegaCon panel, Carlos Valdes was asked about his opinion on how Barry’s attempt to save his mother from the Reverse Flash would have an impact on the timeline. He said “All I’m going to tell you is things are going to be different, way different. Not in a bad way; I think in a really exciting way, and it’s that difference that’s going to inform Barry’s trajectory throughout the season, and I think people are going to like it.
Matt Letscher (Reverse Flash/Eobard Thawne) said in an interview “Barry is starting to get unfolded in this new timeline so he is losing memories of the previous timeline”.
Keiynan Lonsdale said, “Kid Flash is a big part of Flashpoint.”
Candice Patton said, “Barry’s dynamics with Joe and Iris will change significantly.”
Jesse L. Martin said on the red carpet “This Flashpoint thing will blow your mind as characters are still the same people but everything is a little different, so it’s almost like playing a new character.”
Danielle Panabaker said, “We will get to know more about Caitlin’s background, for instance, her relationship with her mother.”
Tom Cavanagh said, “The conflict in Flash season 3 has been ratcheted to a new level.”