At long last, the circumstances behind one of the most highly anticipated TV crossovers of the year have been revealed. After announcing that the CW’s “The Flash” lead would appear on CBS’ “Supergirl,” fans have finally learned how both worlds will exist at once and what adventure will bring the DC Comics duo together in the first place. 

“Supergirl” is not a drastically different show from “The Flash” in terms of tone, which is why so many people wanted to see them team up. However, each show comes back-loaded with a deep canon history that wouldn’t really mesh well with one another at this late stage in their development. After all, if The Flash (Grant Gustin) lived in the same world as Supergirl Kara Danvers (Melissa Benoist) and her cavalcade of allies and villains, but simply never acknowledged them, it would be weird. How then will the scarlet speedster make his way to National City in the episode titled “World’s Finest”? 

The Flash/Supergirl Barry Allen (Grant Gustin) of "The Flash" will crossover with Kara Danvers (Melissa Benoist) of "Supergirl" on March 28. To promote the event, CBS released this poster based on the cover of DC Comics' "Superman #199." Photo: CBS

“Kara gains a new ally when the lightning-fast superhero The Flash (Grant Gustin) 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,” the episode's official plot synopsis from CBS reads. 

The announcement came with the above teaser image, which Variety notes is designed as an homage to DC’s “Superman” issue 199, which saw a race between The Flash and Superman. While the synopsis teases a lot, the most important takeaway is that it reveals the circumstances that will bring the heroes together. Throughout Season 2 of “The Flash” Barry Allen and his friends have been dealing with the discovery of alternate universes, mainly one they call “Earth-2.” The gimmick essentially means that The Flash is capable of traveling between several different versions of reality. It seems that, in the March 28 episode, he will find his way to the one where Supergirl is doing her heroic thing. As a result, after Allen helps Danvers take down two villains, he’ll likely return home to Central City, and the CW, with no larger canon implications to deal with. 

“Watching the two of them click, that friendship is instant,” executive producer Andrew Kreisberg told TV Insider. “Seeing them be so jazzed about each other is really just fun and it’s led to all sort of funny scenes and funny lines and funny reactions from everybody else.” 

Will you be tuning in for the “Supergirl” crossover on March 28? Comment below or tweet your DC superhero thoughts to @TylerMcCarthy