“Hell on Wheels” fans are going to have to adjust to an all-new Naomi in Season 4. Siobhan Williams was introduced only last season, but she is already leaving the show. The AMC series was unable to resolve scheduling conflicts with Williams’ other show, ABC’s “Black Box,” so it recast MacKenzie Porter for the role.

Showrunner John Wirth talked to Entertainment Weekly about the change, explaining how they decided to handle the situation.

“We were kind of desperately considering how we should handle this: Should we recast? Of course, whenever you have that conversation, the two [Darrins] situation is always brought up. It was not my first choice, but we went ahead with it, and I think we were really lucky to get MacKenzie,” Wirth said.

Wirth was referring to the recasting of Darrin on "Bewitched" in the 1960s. Actor Dick York played the character from 1964 to 1969 until a back injury forced him to quit. York was replaced by Dick Sargent, but the unexplained switch caused ratings to fall.

Of course, plenty of shows have recast roles since “Bewitched.” “Game of Thrones” recast Daario Naharus between Season 3 and Season 4, which was a little confusing for some. Ed Skrein originated the role, but the smaller Michael Huisman took over (and they didn’t even give him Skrein’s wig).  "True Blood" also featured a switch-up, replacing Luke Grimes with Nathan Parsons for the role of James in Season 7. The “Hell on Wheels” recast shouldn’t be nearly as visually confusing. Porter, 24, is a blonde Canadian and at least bares a vague resemblance to Williams. Even the show’s music supervisor didn’t notice the change.

“She plays a bit older, I think," Wirth explained. "But when we were doing music spotting the other day, Kevin Kiner, who does the music for us, said, ‘Boy, Naomi’s changed a little bit since last year.’ I said, ‘Yeah, she’s a year older.’ He said, ‘Amazing.’ I said, ‘But you know it’s a different actor, right?’ He said, ‘What???’ [Laughs] He couldn’t tell.” 

According to Wirth, Porter has the acting chops to tackle the part. "She’s a helluva actress and has really grabbed onto this part and brought a soulfulness to it," the showrunner added.

This casting change won’t slow down Naomi’s storyline at all. Last season ended with Naomi pregnant after one night in the barn with Cullen (Anson Mount), and Cullen marrying her out of a sense of honor. Wirth plans to pick up Season 4 right where they left off.

[Click HERE to see Mackenzie Porter as Naomi on "Hell on Wheels."]

“Hell on Wheels” returns to AMC  Aug. 2 at 9 p.m. EDT. How do you feel about recasts? Sound off in the comments.