When The CW’s “Crazy Ex-Girlfriend” returns for its fourth and final season this fall, it will do so with a “reimagining” of the character of Greg.

Played originally by Santino Fontana in the freshman year, the character was involved in a love triangle with Rachel Bloom’s titular character, Rebecca Bunch, and her childhood sweetheart-turned-hopeful-adult-love Josh Chan (Vincent Rodriguez III). In the fourth and final season, he will be played by Skylar Astin.

Co-creator and showrunner Aline Brosh McKenna shared at the Television Critics Assn. press tour panel for the show Monday that they always planned to bring the character back, but when Fontana did not sign on for a full second season, they “jammed” the resolution they wanted for Greg into the first four episodes and “that completed his arc.”

“In thinking about bringing him back, we knew right away that it would be a reimagining, and that’s part of the story,” McKenna says, admitting the “first thing” they did when they realized that was to reach out to Fontana.

“With an actor leaving suddenly, it left this exciting gap. His character’s almost become like lore in the show,” Bloom added. “We have this opportunity to bring back this mythic figure and look at him in a new way.”

Bringing in a new version of Greg now feels “not only a big leap and feels experimental and playful for our show,” said co-creator and star Rachel Bloom, “but as you see when the show airs it will be kind of a great statement on how our perception of people changes. … Greg is a barometer of [that] because Rebecca has not seen him for two years.”

Since the show is a “first-person show in many ways,” McKenna said, the episodes that feature Astin will dive deeper into that point of view.

“It’s not a Becky on ‘Roseanne’ situation,” Bloom says. “Rebecca’s going to call it out and be like, ‘This person is different, what the f—?'”

Bloom went on to say that “as a fan of television,” it means a lot to her to be able to offer a complete story. “Crazy Ex-Girlfriend” was crafted from the beginning with a four-season arc.

“Every season was a different lens of what it meant to be a crazy ex from the inside out,” Bloom said. “There are network executives around town that know how our series ends if they remember or care — because they passed.”

Both Bloom and McKenna pointed out that every season of the show has felt like a “mini new show” but the fourth and final one combines “a culmination of all four years” with “starting from scratch.” After all, in the third season finale, Rebecca finally recognized the problematic nature of a lot of her behavior and stood ready to take responsibility for her actions — even if it meant jail time.

While Bloom noted that the first season launched Rebecca’s “inner chaos” as a catalyst for story, the fourth season will see her more “settled, and then the chaos starts happening around her, and she finds herself in the middle of a bunch of romantic comedies.”

True to that theme, the final season’s theme song will be a sendup of sorts to traditional 1980s sitcoms, “including clip shows,” Bloom said. “It’s a mix…that feels like it’s opening in a Doublemint gum commercial,” she said. “Really the essence of it is how it’s hard to boil someone down into a single theme song. … [And there is] an element of it that will be changing every episode, which will be fun for fans.”

Before the series comes to an end, Bloom will write her first episode of the series (the premiere), as well as direct (the penultimate). McKenna is also directing again, this time the series finale. Also, the show will pay off a number of things the cast has wanted for awhile, including “more group numbers,” the return of Patton Oswalt (“who will sing a song,” Bloom revealed) and a Rodgers & Hammerstein number.

“That’s to please all the millennials out there,” Bloom joked.