Fans of CW's Arrowverse are very much accustomed to alternate versions of various heroes and villains popping up, whether it be Black Siren from Earth-2, Jay Garrick from Earth-3, or even Harry Wells from Earth-19. However, it appears those behind the scenes over at "Supergirl" -- which is set on a different Earth from the one seen in "Flash" and "Arrow" -- aren't quite as keen on the idea of having any doppelgängers appear in National City.

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Yesterday, "Supergirl" producer Andrew Kreisberg spoke with IGN and was questioned on the possibility of an Earth-1 version of Kara Zor-El showing up on "The Flash" or "Arrow," or whether alternate versions of characters from "The Flash," "Arrow," or "DC's Legends of Tomorrow" may pay the Girl of Steel a visit on "Supergirl." According to Kreisberg, though, showrunners have chosen to avoid going this route for fear of opening up a massive can of worms:

"The problem with that is it feels to us like if we do that once, we're going to open the floodgates of insanity," said Kreisberg. "It's like Supergirl's over here, and it's its own show. Technically speaking, it's just another Earth, the same way Earth-2 is or Earth-3 or Earth-19. So technically speaking, there should be an Alex Danvers on Earth-1, or Earth Prime. But if we start doing that, I just feel like... Not that all hell hasn't broken loose already, but unless we had a really good story for it..."

Kreisberg commented further, citing how plot devices such as alternate Earths can easily become crutches rather than tools. "The more you start to do that stuff, the more it can very easily become annoying or like, 'Here we go again.' Even on Supergirl itself, like Chyler [Leigh] got the opportunity to play a White Martian [impersonating Alex]. Already built into our show, there's already characters playing different versions of themselves. It could very easily spiral out of control."

While some may be disappointed that the Arrowverse seemingly won't include doppelgängers either from or in National City, Kreisberg's sentiments certainly aren't unwarranted. After all, it was the over-reliance on parallel worlds as storytelling devices that caused the DC Universe to become convoluted and nigh unapproachable for new readers, forcing DC to wipe their entire multiverse from existence in 1985s "Crisis on Infinite Earths."

All things considered, it seems as though, at least for the time being, "Supergirl" will continue to occupy its own space within CW's Arrowverse. However, things could certainly change by the time the next four-show crossover takes place.

Starring Melissa Benoist as the Girl of Steel, "Supergirl" airs Mondays at 8 pm ET/PT on The CW. The series also stars Mehcad Brooks as Jimmy Olsen, Chyler Leigh as Alex Danvers, Jeremy Jordan as Winn Schott, David Harewood as Martian Manhunter and Chris Wood as Mon-El.