Just in case you thought Once Upon a Time had run out of fresh magic after six seasons and 130 episodes, Edward Kitsis, Adam Horowitz, and the rest of the Storybrooke gang created "The Song in Your Heart," a musical extravaganza that will play out in flashbacks accompanying Hook (Colin O'Donoghue) and Emma's (Jennifer Morrison) present-day wedding.

"The one request we've had since the show began is, 'when are you going to do a musical?' — because obviously, fairy tales lend themselves to that," Kitsis explains in a behind-the-scenes clip released by ABC. "We thought this was the perfect opportunity to make their wedding even more special."

The track list for Once Upon a Time's musical episode has been revealed

The duo enlisted the help of Broadway vets Alan Zachary and Michael Weiner, who were already fans of the show, to write original musical numbers that Ginnifer Goodwin feel honor Once's story in a very organic way.

"Instead of it being that we stop the flow of action to tell you how we feel, [the songs] really further both our emotions and the plot," she says, adding that "even the dancing supports the acting."

Among the numbers featured are a lyrical take on Emma's theme that Morrison claims will help fans "understand what it means to Emma ... that it is actually able to break a curse," a Hook-and-Emma wedding duet, a "wicked" Zelena (Rebecca Mader) solo, a Snow-and-Charming partner dance, and an Evil Queen solo Lana Parrilla describes as "David Bowie meets Rocky Horror Picture Show."

"I have, I think, the only rock number," Parrilla explains with a smile. "She's full-on glam rock."

Despite the exciting theatrics, the cast maintains that Zachary and Weiner's musical numbers honor the saga of the Charming-Mills-Swan family ... and of course, add a hefty dose of good old fashioned Disney magic.

"If any show, realistically, is going to do a musical episode, this show is the perfect candidate," O'Donoghue explains. "It's Disney! It just fits in our world."

"They did an amazing job," Morrison concludes. "Every once in a while, you get to a place where you're like, 'everything feels right about this' ... everything about it so far has felt so authentically right for Once Upon a Time."

Once Upon a Time's musical episode, titled "The Song in Your Heart" will air on Sunday, May 7th at 8/7c on ABC.