Simpsons to Premiere with First-Ever Musical Episode, Kristen Bell and Revamped 'Treehouse of Horror'

It may be the longest-running comedy in television history, but "The Simpsons" isn't content to sit back and rest on its laurels. Instead, the venerated animated series continues to innovate as it heads into its 33rd season.

Speaking at the show's Comic-Con@Home panel, as covered by Deadline, executive producer Matt Selman teased two new innovations, including the show's first-ever, full-blown musical episode. To celebrate the milestone moment, Kristen Bell has been tapped as the new voice of Marge Simpson -- her singing voice, that is.

The "Frozen" star joins long-time voice actress Julie Kavner in bringing the Simpsons family matriarch to life for "The Star of the Backstage," a premiere described by Selman as "the most musical episode we’ve ever done ... like a Broadway musical of an episode with wall to wall music.”

The premiere episode will feature several original songs, though we're not sure any of them could be as catchy as when the family released its first full-length album, "The Simpsons Sing the Blues," way back in 1990.

The show has featured plenty of original songs over the years, but this is their most ambitious foray into the music, with a full-blown, wall-to-wall, old-school musical format from start to finish.

Selman described the premiere by saying, "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."

Explaining why the shift to Bell from Kavner, who has sang for Marge before, Selman told EW, "The only place Marge sang beautifully was in her head, so she has a magical inside singing voice that only we can hear."

The traditional Halloween episode also sees a major shift after more than three decades, with executive producer Al Jean revealing that instead of the traditional three off-the-wall segments, "Treehouse of Horror XXXII" will be expanded to five.

Jean and Selman further teased a few other upcoming big moments for the series, including a possible romance for Moe the bartender, as well as a two-part "love letter to the show 'Fargo' and the world of streaming television," per Selman.

Upcoming guest stars beyond Bell include "Crazy Ex-Girlfriend" star Rachel Bloom, Timothy Olyphant, Cristin Milioti and Brian Cox.

You can catch the entire panel below, including the first-look at one of those "Treehouse" segments at 34:05 -- inspired by the macabre works of writer-illustrator Edward Gorey -- in its entirety.