ET on ABC, is titled “The Song in Your Heart.”

Here’s what else you better know:

ENTERTAINMENT WEEKLY: Why is everyone breaking into song?

The singing and the musical is tied directly to Emma.

JOSH DALLAS, JENNIFER MORRISON, GINNIFER GOODWIN

Credit: Jack Rowand/ABC

Why did you decide to do a musical for Emma’s wedding?

When we started talking about the musical, we wanted it to be a special episode.

We thought Emma’s wedding felt like the natural milestone for us.

HOROWITZ:It felt like the right place.

We’re trying to move toward something.

It builds to that wedding, whichlike everything in the episodewe hope is filled with a few other surprises.

What can you tease for some of the songs we’ll be hearing?

KITSIS:The songs are all original.

They’re specific to each character.

The composers did an incredible job.

So we’re really excited about it.

KITSIS:And they’re catchy.

Are the characters aware that it’s odd that they’re singing?

Do you go meta in that sense?

KITSIS:I would say yes.

HOROWITZ:Yup, it’s not just like singing and nobody acknowledges that songs are happening.

When it came to singing and dancing, was there anyone in the cast who surprised you?

KITSIS:Yes, Pongo really good.

One question that’s come up a lot: Is Rumple going to sing?

KITSIS:For that, we’ll have to wait until the musical airs!

Read our postmortem with Rebecca Mader on Zelena’s sacrificehere.Once Upon a Timeairs Sundays at 8 p.m.