When the various DC Comics shows return to television this fall, the majority of them will be found on one network – The CW.
It has also been confirmed that there will be a musical crossover between The Flash and Supergirl, that stars Glee alumni, Grant Gustin (who plays The Flash) and Melissa Benoist (who plays Supergirl).
There are some characters who show up in her episode, but the story begins with The Flash episode and goes to Arrow and Legends of Tomorrow.
In fact, we already know there will be at least one massive crossover that includes characters from Supergirl, The Flash, Arrow, and Legends of Tomorrow.