Two "Glee" alumni are set to fire up the screen really soon when their hero forms' alternate universes collide.

Every single teaser and detail dropped trend effortlessly, and Deadline shared the episode synopsis titled "World's Finest." Set in National City, "Kara gains a new ally when the lightning-fast superhero The Flash suddenly appears from an alternate universe and helps Kara battle Siobhan, aka Silver Banshee, and Livewire in exchange for her help in finding a way to return him home."

Aside from the 10-second clip showing the heroes, pictures of them together have already made the rounds. One that excites viewers most is that which depicts the two preparing to race to find out who the real speedster is. Comic fans were quick to point out that the scene was derived from what is originally a Superman arc whose edition title is the same as the episode's crossover.

In "The Flash's" universe, it has been established that his speed does not only allow him to travel through time but it opens portals to different worlds as well. While it has not yet been revealed how Grant ends up in Kara's world, chances are that his quest to find a way to re-enter Earth-2 brings him there. This possibility has already been introduced as Supergirl was briefly shown when Barry entered Earth-2 with Cisco and Dr. Wells.

The two main antagonists for the crossover episode have met Kara in the workforce. Livewire was a reporter struck by lightning and eventually gained superpowers. She was out to revenge on Cat when Supergirl came and found a way to disable her electrical abilities. It appears that she escapes from detainment and is now set to avenge herself from Supergirl.

On the other hand, the latest "Supergirl" episode has shown Siobhan getting fired after being in competition with Kara for Cat's attention. Fans have been waiting for her to reveal her alter ego Silver Banshee and are also dying to find out if she eventually becomes friends with the heroine like she did in the comics.

The most-awaited super episode is scheduled to air on March 28.