Butch Gilzean or Cyrus Gold (Drew Powell) will return to “Gotham” Season 4 as a zombie named Solomon Grundy. Fox

How does a person become a zombie in Gotham City anyway? “Gotham” Season 4 will explain just how this happens through Butch Gilzean, who was shot by Barbara Kean during the Season 3 finale.

According to executive producer John Stephens, Butch (Drew Powell) isn’t actually dead yet, but he’s left in a vegetative state at Gotham General hospital. Unfortunately, Gotham City does not really take good care of its patients.

“And so in order to clear up space for more beds, the administrators at the hospital have him dumped in Slaughter Swamp, as one does in Gotham. So he emerges reborn out of Slaughter Swamp as the character we know as Solomon Grundy,” Stephens told Entertainment Weekly.

Surprisingly, the first person Grundy would talk to in his new form is Butch’s former enemy, Ed Nygma (Cory Michael Smith). He does not remember all the nasty things Ed did to him in the past, so they team up.

“We begin the story of a very unlikely friendship between these two who are sworn enemies but now, all of a sudden in Season 4, are best friends as they move through Gotham,” Stephens teased.

The two of them will not be alone, since they’ll also be teaming up with Dr. Leslie “Lee” Thompkins. Stephens told Cinema Blend that she’ll be “very different” next season, and the three of them will “form this weird little family.”

Another friendship to be formed next season will be between Selina Kyle (Carmen Bicondova), Tabitha Galavan (Jessica Lucas), and Barbara (Erin Richards). Tabitha and Selina had little interaction over the past few seasons, but now, it will be Tabitha teaching Selina the ropes so she could transition into the Catwoman. “Those skills that you associate with grown-up Catwoman, we’re going to see Tabitha start teaching her at the beginning of this year,” Stephens told TV Insider.

As for Babs and Tabs, they’ll bury the hatchet and even form a new business together. At the same time, they’ll strive to be the best mentors for Selina.

“Gotham” Season 4 will premiere on Sept. 21 on FOX.