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‘Supergirl’ Season 2 Finale Introduces Mysterious New Villain

Is it Doomsday? Reign? Someone else?

Spoiler: Details from Monday’s “Supergirl” season 2 finale.

“Supergirl” capped off its emotional Season 2 finale with a new mystery that sets up the third season of the CW superhero drama.

Flashing back to 35 years ago, the day Krypton died, we travel from where Superman and Supergirl were placed in pods to travel to Earth, to the opposite side of the planet, to find that another baby was being prepped for the same flight.

Hooded figures lay the baby down, then seem to feed the tiny creature a fingertip smeared with some blood.

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Who is this mysterious newcomer, who would be a grown adult in present day?

The baby drinks blood, which could point to iconic Superman villain Doomsday – last seen in “Batman v Superman.”

Another clue comes from the hooded figures, who discuss the baby as “it” rather than him or her.

“It will grow strong on earth,” one says. “It will reign.”

Reign is the name of another DC comic book villain, a “worldkiller” created by a group of Kryptonian scientists.

Elsewhere in National City, Supergirl saved the world once again, but this time at great personal cost. Choosing to detonate a weapon that would make Earth uninhabitable for all Daxamites, Kara says goodbye to her boyfriend Mon-El (Chris Wood), sending him off to the safety of space as she continues to do her duty as a hero.

A more happy ending was in store for Alex (Chyler Leigh), who, at Kara’s urging to hang to her own love, spontaneously proposed to girlfriend Maggie (Floriana Lima).

Meanwhile, “Supergirl’s” greatest mystery – does Cat Grant (Calista Flockart) know Supergirl’s true identity? – was also solved as we finally got confirmation that Kara’s boss does indeed know about her star reporter’s secret identity.

“Supergirl” will return for Season 3 on Monday nights in the fall.