The Flash: 24 WTF Moments
15. Barry Was Present During General Zod's Attack
As a result of Prime Barry's multiversal meddling, General Zod (Michael Shannon) and his army show up in this timeline, at which point Prime Barry recounts Zod's attack on Metropolis in his own timeline - basically, the events of Man of Steel.
Barry reveals that he'd received his Flash abilities a short time before the attack and was actually present during the catastrophe.
At this point, a flashback shows a younger, wildly inexperienced Barry in a prototype Flash suit as he attempts to help rescue civilians from Zod's massacre.
In one pivotal moment Barry does manage to save a young boy, though regrets also being unable to save his father, who is killed by one of Zod's ships moments later.
You can call it a retcon if you want, but at least it makes total sense to place Barry within the events of the DCEU's very first movie.