When CBS first announced their plans for a "Supergirl" series, fans immediately began wondering if The CW's roster of heroes ("Flash," "Arrow," etc.) would be showing up at all. Though producer Greg Berlanti downplayed this possibility, the so-so ratings of "Supergirl" have opened the door for a "Flash" crossover during sweeps week in 2016. However, that may no longer be the case.

Executive producer Andrew Kreisberg recently told The Hollywood Reporter that there are some tricky legal hurdles to jump through in terms of Kara Zor-El and Barry Allen, or any other characters, sharing the screen.

"There's always those late nights, delirious, semi-high on pizza where you're like, 'You know what would be really cool?' If...'" Kreisberg said. "But right now there is no legitimate actual plan to bring ['The Flash's'] Cisco [Carlos Valdes] onto 'Supergirl' or to bring ['Supergirl's'] Winn [Jeremy Jordan] onto 'Legends [of Tomorrow].' First of all, we don't even know if we could, legally. And quite frankly, just making the 'Arrow'-verse which is what we call 'Legends,' 'Flash' and 'Arrow' work and then making 'Supergirl' work, it's enough of a challenge without having to add a fourth player."

This is the first we've heard of legal roadblocks preventing a crossover. Both CBS and The CW are owned by CBS Corporation, leading us uninformed viewers to believe that a shared cross-network universe is possible. But Kreisberg's comments support what Berlanti said last week after a screening of this week's "Flash"/"Arrow" two-part crossover. Berlanti was asked if a CBS/CW crossover was in the works, to which he said one had not been planned "only because we just received the [full season] pick up. Not at this point."

Alas, fanboys and girls can dream.

"Supergirl" airs on Mondays on CBS. "The Flash" and "Arrow" can be seen on Tuesdays and Wednesdays, respectively, on the CW.