Shortly after CBS’Supergirltransitioned to The CW for its second season, rumors started spreading about a crossover with this program and the CW’s superhero lineup,Arrow,The FlashandLegends of Tomorrow. While that program has since been confirmed, it was also revealed that there will also be amusical crossoverbetweenThe FlashandSupergirl. Both of those show’s stars,Grant GustinandMeissa Benoistare accomplished singers who have both appeared onGleebefore their superhero shows, and today we have more details about both crossovers.

It was previously revealed that theFlash and Supergirlmusical crossover will largely feature cover songs, but the producers are trying to find a way to include some original songs as well.IndieWirecaught up withGreg Berlanti, who serves as an executive producer on all four shows, who revealed that this crossover episode has already been written.

“We just finished writing the fall crossovers. And now we’re trying to figure out how to produce them. That’s probably the most challenging thing we do all year. And now we’re doing it across three shows! But next week we’ll have to start talking about clearing music. I have a few ideas for tone and style in my head but we’re just starting to talk about what that can be. I do want to try and get an original piece of music written. As we make a deal on that we’ll probably make some announcements on the original songs.”

When asked if they have been talking withLin-Manuel Miranda, who created and starred in the Broadway sensationHamilton,Greg Berlantiwouldn’t confirm, but he did say that he has spoken with someone they are “really excited about.” He also confirmed that the musical crossover will span two episodes, withSupergirlairing on Monday nights at 8 PM ET andThe Flashairing on Tuesday nights at 8 PM ET. When asked about the four-show crossover,Greg Berlanticonfirmed thatSupergirlwill be featured, but it will largely focus onArrow,The FlashandLegends of Tomorrow.

“You really are trying to run a single production across three different productions. But they’re run as three separate entities. We have to figure out when we’re borrowing one actor from where. We’re telling one cohesive story;Supergirlwill participate, but the storyline doesn’t actively begin there. There are some characters who show up in her episode, but the story begins withThe Flashepisode and goes toArrowandLegends of Tomorrow. We’re just getting into designing the bad guy for it, and we start now but it doesn’t air until the end of November. We will put a lot of time between now and then figuring out visual effects sequences. Just today I was holding the three scripts back-to-back - that’s 180 pages of material. It’s a three-hour story, almost a miniseries.”

There will be a few characters likeKatie Cassidy’s Black Canary andWentworth Miller’s Captain Cold who have signed deals with The CW that makes them series regulars on all four shows, so they will certainly figure in to the crossovers.The Flashwill kick off TheCW superherolineup on Tuesday, October 4, followed by {Arrow{ on Wednesday, October 5, {31} on Monday, October 10, andDC’s Legends of Tomorrowon Thursday, October 13. It hasn’t been confirmed when these crossover shows will air, but hopefully we’ll find out very soon.