If there's one thing "Gotham" fans should know by now, it's that nothing happens in Gotham City that's merely a coincidence. So when the doppelgänger of Ed Nygma's (Cory Michael Smith) former flame Kristen Kringle (Chelsea Spack) surfaced this Season 3, alarm bells went ringing.

The doppelgänger, Isabella, seems too good to be true for Nygma. They have so many things in common, and she gets his beloved riddles. And unlike Kristen, she isn't creeped out by Nygma. But who is she really?

According to Bustle, Isabella might be one of Hugo Strange's experiments. It's possible he resurrected Kristen from the dead and made her think she's Isabella. After all, he did the same thing to Theo Galavan. The only catch here is that Nygma chopped Kristen's body to pieces, so it would have been quite a task for Strange to stitch her up.

Another theory is that Isabella is Kristen's relative who is out for revenge. The show never touched on Kristen's backstory, and she seems pretty unattached, family-wise. But she could have a twin sister who wanted to unravel the truth about her disappearance.

On the other hand, 2 Paragraphs suspects that Isabella is actually a Russian assassin named Isabella Cheranova, also known as Echo. In the comic books, Echo had a device implanted in her head which allowed her to telepathically read the thoughts of people and computers.

This theory holds up because Isabella was able to make Nygma fall in love with her after just one night. She might be hired to kill off Mayor Oswald Cobblepot (Robin Lord Taylor), so she's using Nygma to get close to him. In the end, Nygma might be forced to choose between Isabella and his boss.

"Gotham" airs every Monday at 8 p.m. ET on Fox. Gotham Ed Nygma experienced a blast from the past when he met Kris Kringle's doppelgänger, Isabella. Photo: Fox