Warning: Spoilers ahead for The CW Arrowverse crossover Crisis on Infinite Earths.
The Flash had found himself separated from the remaining Paragons (characters that represent ultimate level of heroism) when the Anti-Monitor attacked him inside the Speed Force.
Gustin's Allen runs into STAR Labs wearing his Flash costume, only to be shocked to discover Miller's Barry Allen there too. This officially connects the TV and film universes of DC Comics.
As expected, Flash fans showed their excitement for the cameo on social media.
"I am literally losing my mind right now. Biggest crossover ever - DC and CW just did it," one user tweeted.
"Best. Crossover. Ever," another fan tweeted.
The final episode of the crossover event airs Tuesday night with Legends of Tomorrow.