It turns out The Boys‘ Billy Butcher really is his own worst enemy.

Following season 4’s sixth episode, showrunner Eric Kripke spoke with Entertainment Weekly about the episode’s big Joe Kessler twist and what it means for Butcher’s future. Where much of season 4 portrayed Kessler as an old friend aiding Butcher’s war against Homelander, “Dirty Business” revealed him to be a manifestation of Butcher’s darkest impulses spawned, like the hallucination of his wife Becca, from his Temp V brain tumor. This, according to Kripke, ties into The Boys‘ recurring motif of Butcher and Homelander “wrestling with whether they’re human or whether they’re monsters. Kessler represents the monster side and Becca represents the human side of Butcher. Those two sides are at war with themselves, but they’re all Butcher.”

Much about Kessler’s motives — including the identity of Jeffrey Dean Morgan’s character — were kept shrouded in mystery leading up to season 4’s release, though Kripke insisted he was always crucial to the story The Boys‘ writers had in mind for Butcher. “We wanted Butcher to really be dealing with his light and dark sides, and yet he was so isolated for so much of the story that we needed a way to dramatize it. The notion of literally the angel and devil on his shoulders came up pretty soon,” he explained. Kripke also praised producing director Phil Sgriccia for putting together the big Fight Club-esque reveal scene where Butcher learns the truth, stating, “He laid out a rule to all the different directors: Whenever you shoot a scene with Jeffrey and Karl, you have to do a take where Jeffrey steps off and reads the lines off camera so that there’s nobody there. He said, ‘Because I know as an editor I would want that when that reveal comes.’ It’s a testament to how smart Phil is.”

The Boys and Gen V Can Be Enjoyed On Their Own

Additionally, the Kessler twist teased an ethical dilemma for Butcher’s quest to create a Homelander-killing anti-supes virus, learning that such a weapon would have to go airborne and, as a result, kill everyone on Earth with Compound V in their body. The virus was first introduced in last year’s college spinoff Gen V as a secret lab experiment created by Godolkin University, with season 4 referencing the show’s events and even featuring cameos by two Gen V characters in a recent episode. However, despite including these callbacks, Kripke insisted that both shows can be watched on their own and a future The Boys/Gen V team-up story remains unlikely.

The inclusion of Morgan as Kessler marks Kripke’s second major Supernatural casting after Jensen Ackles, who played Soldier Boy in season 3 and Gen V. Meanwhile, Ackles’ co-star Jared Padalecki — whose CW show Walker ended last month after four seasons — recently discussed the possibility of joining The Boys‘ cast for its fifth and final season.

New The Boys season 4 episodes stream on Thursdays on Prime Video.