Long before Supergirl premiered, CBS cast doubt on the likelihood of Kara crossing over with Arrow or The Flash just yet, an idea recently revisited when executive producer Greg Berlanti shot down a rumored Barry Allen appearance. Some fans had hope that the timeline-hopping Legends of Tomorrow might make crossover potential a bit easier, but producer Andrew Kreisberg isn’t sure they’re even legally allowed to play with Supergirl.

Where last night’s conclusion to the two-part Arrow and Flash Legends of Tomorrow setup put the final pieces in place for the 2016 series, The Hollywood Reporter confirmed with executive producer Kreisberg that Legends’ time-travel and dimension-hopping nature wouldn’t facilitate any easier crossover with Supergirl, or even the supporting characters. The issue isn’t so much that Kara would theoretically have to exist on another Earth well-aware of Superman, but rather the legality, and logistics:

There’s always those late nights, delirious, semi-high on pizza where you’re like, ‘You know what would be really cool? If …,’ 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.

That will certainly dishearten fans of either universe, though Supergirl still has plenty to look forward to in the coming months, including a 13 year-old Clark Kent and an additional seven-episode order, one of which will be directed by Punisher: War Zone and Arrow helmer Lexi Alexander.

Legends itself has plenty of bonkers DC lore to play with, but will Warner Bros. ever unite The CW and CBS universes for a full crossover?