Marvel fans have been left surprised after finally hearing a comic book character mentioned in the new series Agatha All Along—and the miniseries showrunner suggesting that it will have some significance moving forward.

The third episode of the new Marvel show, which has been described as “perfect” and “spellbinding” in early reviews, has dropped the name of the supernatural villain Mephisto, who has long been teased to arrive in the franchise.

Mephisto is a demon character based on Mephistopheles from the Faust legend. He was created in 1968 by Stan Lee and John Buscema and has primarily been an adversary of Ghost Rider and Silver Surfer, but he has also clashed with Spider-Man, Doctor Strange, and Scarlet Witch.

Fans were left disappointed after the character failed to appear in WandaVision and Loki, but Mephisto finally looks set to make an appearance in Agatha All Along after Sasheer Zamata’s character, Jennifer Kale, hypothesised that the mysterious Teen, played by Joe Locke, could be “an agent of Mephisto.”

Following the debut of the episode on Disney+, showrunner Jac Schaeffer told Entertainment Weekly: “With these shows, so often there is something that is at once a joke and a wink and a nod, and actually has something legitimate underneath it.”

Schaeffer added: “As we all know, Mephisto is a character who is very much wrapped into Agatha’s storyline. I mean, people have to watch, but we’re always playing with the audience in that way.”

Understandably, fans were delighted to finally hear Mephisto’s name mentioned.

One fan joked: “The writers were tired of hearing the Mephisto theories, so they said ‘here you go, damn!’”

“THEY FINALLY MENTIONED MEPHISTO!” wrote another ecstatic fan.

Others shared memes about their excitement.

A popular fan theory circulating regarding Mephisto’s involvement in Agatha All Along is that Aubrey Plaza’s character, Rio Vidal, or the Green Witch, is somehow related to the villain. References to Mephisto’s son in the comics, Blackheart, have been mentioned twice in the show already, with some fans concluding that Plaza is portraying a version of the character.

Elsewhere, the show’s main star, Kathryn Hahn, has spoken about the opening scenes of the spin-off series where she is seen naked and wandering the suburban streets from WandaVision.

“I thought it was good to see her as stripped down, literally, as we possibly could, which spoke to her powerlessness at that present moment,” Hahn told Variety.

“[Agatha has] been stripped of all her power at this point in the series. I mean, she really had nothing at that point, and so it became about illustrating that gap between that moment and her finding her power again.”