The story of Barry Allen’s time travel in THE FLASH will establish a completely new DC cinematic universe, drawing inspiration from a significant event in the comics.
Inspired by the Flashpoint Event

Taking inspiration from the Flashpoint event, The Flash inadvertently “rewrites” the timeline, leading to a myriad of dramatic changes. According to the details from the trailer, Barry’s mother was murdered when he was young, which has driven him to return to the past in hopes of saving her. However, Barry’s attempt to change the past “creates a new timeline,” resulting in a completely different reality.

In the context of the film, there will be two timelines in The Flash, marked by distinct indicators: one where Barry’s mother is dead (the main timeline) and one where she is alive (the alternate timeline). Both realities will feature two versions of The Flash; however, there will also be other supporting characters appearing due to the multiple timelines Barry has inadvertently created.
Supergirl

In the Flashpoint storyline from DC, The Flash’s return and drastic changes significantly impact the Justice League. In this situation, Superman’s disappearance leaves humanity vulnerable. After crashing into Earth, the Kryptonian child is captured by the government and imprisoned, losing his light.
This presents a great opportunity to develop Supergirl’s narrative in The Flash. In the trailer, Kara Zor-El is shown to be imprisoned, hinting at Superman’s dire circumstances in the original storyline. Consequently, she may have been captured by the government, becoming a test subject in an alternate timeline after crashing to Earth. Additionally, Kara is essential for The Flash’s plans, being the “metahuman” that the main character needs.
The Flash’s Variants

When returning to the past to save his mother, the main timeline’s Flash accidentally encounters another version of himself. Both Barry Allen versions are portrayed by Ezra Miller, yet they possess distinct characteristics.
The existence of two versions of The Flash this time holds significant meaning as it solidifies the concept of a multiverse that has officially formed in the DC films. Together, the two Barry Allens unite to thwart General Zod’s invasion, while also seeking a way to restore the timeline to its original state.

Moreover, a promotional artwork for The Flash hints at the presence of a third version of The Flash, potentially featuring a hidden character (Reverse Flash or The Flash from the future) in the Flashpoint timeline.
“The Old Man” Keaton
Not only Superman but also Batman plays a major role in the narrative when The Flash returns to the past. Gone is the familiar Bruce Wayne portrayed by Ben Affleck; this time, Batman is represented by Michael Keaton in a different role.

The presence of Michael Keaton’s Batman carries significant implications, as it connects to the character’s legacy from Tim Burton’s films, marking a return to the dark knight who has long been absent. Consequently, The Flash is viewed as the next chapter in the journey of Bat-Keaton on screen, potentially serving as a bridge between Bat-Keaton and Bat-Ben.
THE FLASH premiered on June 16, 2023, in formats including 2D, IMAX, 4DX, and ScreenX.