The Good Place and Frozen star Kristen Bell will feature as Marge's singing voice in the first ever all-musical episode of The Simpsons this September.

Brian Cox, Fargo actress Cristin Milioti, and Timothy Olyphant will also feature in the episode, which is entitled The Star of the Backstage.

Details of the first show in 33rd season of The Simpsons were revealed at Comic-Con over the weekend and speaking to Entertainment Weekly, executive producer Matt Selman said that it will be "the most musical episode we've ever done."

He added, "Almost wall-to-wall music. It's like a Broadway musical of an episode with all original songs."

A synopsis for the episode says, "Marge has amazing memories of being the stage manager of her high school musical, Y2K: The Millennium Bug, and decides to restage it with everyone 20 years later for one last show.

"But when her old high school nemesis comes to town, she realizes that her high school memories aren't what she thought they were."

Speaking about Bell taking on a singing part on the show, he added, "We all love Marge's voice [Julie Kavner] but this is the singing voice that's different, let's just say.

"The only place Marge sang beautifully was in her head, so she has a magical inside singing voice that only we can hear. When she sings, it comes out beautiful, like Kristen Bell."

Simpsons showrunners also revealed that this year's Treehouse of Horror special will feature five segments instead of the usual three and that the new season of the show will include a two-part episode called A Serious Flanders, which is described as an "epic love letter to the show Fargo, prestige crime dramas, and the world of streaming television."