In the mid-season premiere of The Flash, the show name-dropped one of the most dangerous Earths in the DC multiverse: Earth-15. In the comics, that’s where a psychotic, evil, and ultra-powerful version of Superman destroyed the planet.

And you thought Nazi Earth-X from the crossover was scary.

Spoilers follow for “The Trial of The Flash.”

While Barry Allen was on trial for murder in “Trial of the Flash,” the rest of Team Flash had to deal with a “bus meta” with growing radiation powers, one that would go nuclear if left unchecked. Barry’s idea is to create a vacuum around the meta, titled Fallout, to contain the blast but the radiation levels soon go critical. The resulting explosion would be like a nuclear bomb — unless they can vent the energy somewhere.

“Earth-15 is a dead Earth!” Harry remembers. “Breach it there now!”

Cisco opens up a massive breach to vent all of the radiation onto an alternate Earth, and the day is saved.

What's on the other side of that breach?

The fact that Earth-15 is confirmed as a “dead Earth” probably piques the interest of DC Comics readers, because that universe has a tragic history. Originally “The Perfect Universe,” it was a blissful planet. The Justice League’s heroes had essentially won the war on crime, and everybody was happy. It’s a shame they were all killed and their Earth destroyed by a version of Superman from Earth Prime.

On Earth-Prime, Superman (originally called “Superboy-Prime) was the only hero. During the landmark, even comic Crisis on Infinite Earths, which cleaned up the comics’ messy multiverse, Superboy-Prime wound up in a Paradise dimension where he mourned his destroyed world and went totally crazy. After escaping in another “Crisis,” he began wandering the multiverse searching for a home he never found, killing anyone who stood in his way, and eliminating all the Supermen out there so he might become the only one.

If the Arrowverse Earth-15 suffered the same fate as what happened in DC Comics, then Superboy-Prime already destroyed the planet and moved on.

Alternatively, after the comics version of Flashpoint, that same universe became known as “Earth 15” (no dash), which was entirely barren of life. So that could be what Wells is referring to, but for him to say the 15th Earth is a “dead” one implies that it used to be “alive.”

Which means that somebody out there killed it. Granted, in the 2007 comic event series Countdown, Superboy-Prime straight-up destroyed the planet, rather than just leave it “dead,” so the Arrowverse’s version doesn’t exactly line up. At the very least, though, this is a nice little Easter egg for comic fans.

Superboy-Prime destroys Earth-15.

We can’t be sure whether or not Superboy-Prime exists out there in the Arrowverse, but we do know that at least one Superman exists in the Earth-38 of Supergirl.

The “Crisis on Earth-X” crossover firmly established that there are a total of 53 Earths in the DC TV multiverse. Dozens of them, we know nothing about. In most cases, the Arrowverse Earths match up to their comics counterparts — we saw as much with Earth-X. If that’s the case with Earth-15, then they better hope Cisco never opens up another breach there again, because Team Flash might not like what’s on the other side.

The Flash airs Tuesdays on The CW at 8 p.m. Eastern.

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