Once Upon a Time is going full musical on Sunday and it will be the most enchanting hour that the show has ever put forth.

The episode features seven original songs from Alan Zachary, Michael Weiner and Once composer Mark Isham and will see the Enchanted Forest versions of your favorite Storybrooke characters finding magic within songs. It's an episode that took months to prepare, between planning, writing songs and filming the ambitious choreography.

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TVGuide.com had the opportunity to talk to Once stars Ginnifer Goodwin (Snow White) and Josh Dallas (Prince Charming) at a recent screening about their experience filming the episode and getting to duet as their famous Disney alter-egos. Check out their answers below, and get ready to swoon on Sunday.

Ginnifer Goodwin and Josh Dallas, <em>Once Upon a Time</em>Ginnifer Goodwin and Josh Dallas, Once Upon a Time

Did the filming of this episode take any extra time because you had to learn choreography, etc?

Josh Dallas: We didn't get any extra time. We still had the same amount of time that we have to shoot an episode, but there was just more work that we had to do on top of what we already were doing.

Ginnifer Goodwin: Starting during the episodes before — I was trying to remember what it was. It was that we were doing crazy Zootopia Oscars stuff at the same time. It was like there was something that was crazy with us flying back and forth, because we started working on the musical...They came to the house at Christmas, the guys, to like audition us, kind of, to test our ranges.

Why did you have to audition for your own musical?

Dallas: Not audition, just to hear our range.

Goodwin: The composers needed to know. No one had ever heard us. I mean I had done a little bit of singing for animation.

Dallas: They didn't ask us if we wanted to do a musical episode. They just assumed that we could sing.

Goodwin: Well no, wait, they did say, "You're going to do a musical episode, how do you feel about it?" And I said, "If you put me in the background with jazz hands, I will serve the story very well." But that's not what happened.

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As huge Disney fans, what does it mean to you to have a duet written just for you that's now part of the Disney universe?

Dallas: I mean it's huge, I think it's huge for us. And what we particularly loved about our number, that it felt, out of all the numbers in the show, that it was the most Disney-esque feeling.

Are you glad that you guys got to sing them as your fairytale characters, and really own the campiness of it all?

Goodwin: We needed to be able to lean in, and I didn't know that would be possible without singing songs that were lifted from historic Disney animated features. But the fact that they — I mean, these composers are brilliant, and I felt that being in fairytale land meant that because we could be a bit more stylized, yeah, we could really dig our elbows in, in a different way than if we'd been — I don't know how we would have done that in Storybrooke. Mary Margaret would have been like, "Don't-- listen-- don't--."

Dallas: The canvas of the fairytale land of it all really lends itself to a musical landscape, so we were lucky.

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Did you end this episode going, "Why haven't we been doing this the whole time?" Or did you end it like, "Oh I see why we haven't been doing this."

Goodwin: I'm glad it's isolated because I think it makes it more special. And I think it lends itself to the finale-ness of the season.

Dallas: We are different from say Galavant or whatever. We're different in terms of how we approach the material. It's definitely better that it was a one-off, I think it just made it more special and more of an event.

Goodwin: And the storyline itself feels — I don't know that we could have stretched out this particular storyline in terms of why the characters start singing. It's so specific. I don't know how long we could have kept that going realistically.

The Once Upon a Time musical episode airs Sunday, May 7 at 8/7c on ABC.