During a Q&A session with reporters following a screening of the three-episode Invasion! crossover earlier this week, Supergirl and The Flash executive producer Andrew Kreisberg was quizzed about the long-lingering question of Supergirl's Earth-1 doppelganger, if she in fact has one.

For instance, he was asked, could fans hope to see Power Girl show up at some point?

Power Girl, for the uninitiated, is an alternate-universe version of Supergirl in the comics, who showed up and for years had either no, or at least scrambled, memories of her life prior to arriving on Earth. She has served as a member of the Justice League and the Justice Society, and co-headlined the title Worlds' Finest with Huntress for a few years following DC's 2011 continuity reboot The New 52.

"We hadn't discussed it formally, but I think that certainly after these three episodes, there's literally no limit to the things that we could do," Kreisberg said. "There's still an endless treasure trove of DC Comics characters, and stories, and titles that we haven't even come close to touching yet. We're certainly not wanting for ideas for the future. We know that they're out there for us."

So far, few major Arrow or Legends of Tomorrow characters have had doppelgangers show up, even on The Flash, where they have already seen a number of alternate Earths. No Supergirl characters have yet appeared outside of Earth-38, the newly-discovered designation of the planet on which that show takes place. This is likely as much a scheduling issue as a storytelling one, although the four-show crossover certainly proves that if there's a script and the will to do it, The CW and the producers will find a way to make the scheduled work.

Arrow, The Flash, and Supergirl will cross over with DC's Legends of Tomorrow this week in "Invasion!" a three-part crossover that starts in the final moments of an episode of Supergirl and then plays through the other series. Based on the 1988 comic book event miniseries Invasion! from Keith Giffen, Bill Mantlo, Todd McFarlane, Bart Sears (who, coincidentally, also drew the Justice League Europe title back when it featured Power Girl), and the crossover -- with its marketing title "Heroes vs. Aliens" -- will closely track the plot of that storyline: aliens will be assembled by The Dominators and descend on Earth to bring an end to the "threat" of Earth's burgeoning metahuman community.

In the comics, the Dominion were secretly hoping to build their own super-race, and as a result created a handful of new superheroes in the course of the story.

In the TV version, rather than assembling a loose alliance of dangerous alien races, the Dominators will apparently be mind-controlling the aliens that join them. That's a revelation that suggests even the heroes might be forced to take one another (or at least the alien Supergirl) on at some point in the story.

NEXT: The Flash, Arrow, Supergirl, Legends of Tomorrow Crossover Trailer / First Look At The Dominators / Invasion! Crossover Promo Photos / Potential The Flash Spoiler Spotted On Set / Will Joe West Die During The Invasion! Crossover? / Enter To Win An Ultra-Rare Invasion! Crossover T-Shirt

Supergirl airs Mondays at 8 p.m. ET/PT; The Flash on Tuesdays at the same time; Arrow on Wednesdays and DC's Legends of Tomorrow on Thursdays. All four series air on The CW. The "Invasion!" crossover will air beginning November 28.