Earlier this week, fans of the "Supergirl" television series were treated to a crossover episode featuring the titular hero from The CW's "The Flash." But, as noted by the show's developers, the episode on Monday could just be the first one to feature other characters from different universes.

In the first season's 18^th episode, titled "World's Finest," Kara Danvers, also known as Supergirl, go up against Silver Banshee and Livewire in National City, IB Times reported. Helping her out in the handicap match is Barry Allen or the Flash, who was able to enter Danvers' universe through a portl.

Together, the two superheroes were able to defeat Silver Banshee and and Livewire and save the city. However, towards the end of the episode, it was revealed that the Myriad has been used to take control of people's minds.

With the episode clearly playing on the multiverse plot point, "Supergirl" executive producer Andrew Kreisberg noted that characters from other superhero shows could also appear in the series. Aside from the Flash, the producer said that Stephen Amell's Arrow as well as the characters from "Legends of Tomorrow" might show up as well.

"We always wanted to do it, just because I think from the day we cast Melissa [Benoist], the notion of her in scenes with Grant [Gustin] or someday, maybe in the best of all worlds with Stephen Amell as well," he told E! Online.

"It's exciting to think of them on screen together," he added.

Technically, the recently released series "Legends of Tomorrow" is one big crossover and spinoff show of "The Flash" and "Arrow" since its characters are also associated with these programs' respective fictional universes.

But, aside from this, the show also has one key element that could make future crossovers highly possible, and that's the Wave Rider. Piloted by time traveler Rip Hunter, played by Arthur Darvill, the Wave Rider is a ship that can also enter other universes.

For Kreisberg, this could probably serve as the main plot point that can bring together the superheroes from the other shows. According to him, this ship can do anything, which includes travelling to other versions of Earth in the multiverse.