Supergirl: Here's where Mon-El's been all this time

Warning: This story contains major spoilers from Monday's episode of Supergirl. Read at your own risk!

Mon-El finally returned to Supergirl on Monday — but he didn't come alone.

The DEO finally discovered that mysterious ship on the National City waterfront, where they found Mon-El (Chris Wood) inside. Yes, he's still alive, but he hasn't just been missing for seven months — for him, it's been seven years.

After being forced to leave Earth in the season 2 finale, Mon-El's pod was sucked into a wormhole, landing him back on Earth, but in the 31st century. Oh, and he's been cured of the lead poisoning thanks to L Corp developing a cure about 400 years from now. (The DEO mentioned his ship had been on Earth for over 12,000 years, meaning Mon-El has been nearby, but in hypersleep this whole time.)

However, it isn't quite a happy reunion between Kara (Melissa Benoist) and Mon-El since he is now married to his shipmate Imra Ardeen, a.k.a. Saturn Girl (Amy Jackson), a member of the Legion of Super-Heroes. It was previously teased that Saturn Girl would assist Supergirl in fighting one of her biggest threats.

That threat is likely Reign, as Samantha (Odette Annable) not only discovered she isn't from this planet during Monday's episode but also unlocked her own Fortress of Sanctuary, where she was disheartened to learn she's actually a supervillain. But in transforming into Reign, Sam's humanity was ripped away from her. Hence, she truly is a Worldkiller now.

Supergirl airs Mondays at 8 p.m. ET on The CW.