The tragic romance of Emma Swan and Captain Hook reached its most devastating moment yet on Sunday night's fall finale of Once Upon a Time. Just as it seemed Emma (Jennifer Morrison) would be sacrificing herself, it was Hook (Colin O'Donoghue) whose life came to an end. But do not fret! Emma's now on a mission, heading to the Underworld to try to save her lost lover. We caught up with executive producers Adam Horowitz and Edward Kitsis to find out why Hook had to die, and what that means for the second half of the season when the series returns March 6.

So why did you murder Hook?

Edward Kitsis: Every season, we try to evolve Emma a little more. She started as a non-believer with walls up who wouldn’t even admit she had a child. [Now] she’s got her family, she’s realized Storybrooke is her home, she’s accepted who she was. She finally opened her heart up to Hook. She finally embraced falling in love, and unfortunately for Emma, everyone she’s ever loved died, and she just didn’t want to see that happen again. So we liked the idea of, what happens when Emma is confronted with the idea of having to let him go? Well, she couldn’t do it. She turned him into a Dark One, the one thing he hated. But their love won out and she ended up having to let him go. But we realized she didn’t as she echoes her father’s line, “I will find you. I will always find you.”

Was doing this to Hook a tough decision for you?

Adam Horowitz: Yeah, it’s always tough when you put characters through really difficult things like death.

Kitsis: But for us, I think the second half is [about], can Emma save him?

Was the actor who plays Hook, Colin O'Donoghue, upset?

Kitsis: Colin has been really excited. He had a lot of fun playing the Dark One; he loved that scene last night with Emma. And I think there’s much more story to be told yet between those two. So I don’t think he was upset because he knows where we’re going.

So it sounds like there's a pretty good chance we'll see him again in the second half of the season in the Underworld?

Kitsis: The real question is: can you bring hope to a place as bleak as the Underworld?

Why did you want to head to or explore this new realm, the Underworld?

Horowitz: Well, I think one of the things that was appealing to us was that our take on the Underworld is not hell. It’s sort of an in-between place. It’s not necessarily filled with villains. It’s filled with all sorts of folks who have unfinished business. What was appealing to us was allowing our characters to face unexpected things from their pasts and have to deal with a lot of people who have unfinished business. And many of them have unfinished business because of our characters.

The internet's been ablaze for awhile now with the news of castings for Hercules, Megara and maybe Hades. Given that you're going to the Underworld, which is in Disney's Hercules movie, is it safe to say they're connected?

Horowitz: I think it’s safe to assume there is some connection. [But] we like to do our own spin. So there’s nods to the Disney movie as well as nods to mythology, and then it kind of goes into the Once Upon soup and becomes our own thing.

Any chance of Pain and Panic showing up?

Horowitz: Um… never say never!

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Might we meet other past dead characters from the show in the Underworld?

Kitsis: Absolutely. We saw last night that Cora was coming back in the teaser for the next half. So we’re absolutely going to see Cora again. We’re going to see the Magic Mirror again, even though he’s not dead. As far as dead people, we’re going to see Cruella, we’re going to see Peter Pan, we’re going to see Cora, we’re going to see Regina’s father...and probably a few other people.

So now Rumplestiltskin has the power of every Dark One ever, was getting him back to being a "big bad" something you've always intended?

Kitsis: Last night, he was very honest when he thought he was going to die. He was being genuine with Belle in saying, "I want you to leave town, and I love you." He was being selfless there, but he had a crime of opportunity when he realized there was a loophole and a way for him to not die. He didn’t do it because he thought he’d see Belle again. He never thought he’d see Belle again. He did it to save his own life because that’s who he is. I think what Hook said to him had a lot of truth in it. He does love that dagger. He did like being the Dark One. Although he’s become a better man, as he warned us since Season 1, he’s a difficult man to love. So I think what makes Rumple tick is always what’s exciting, because just when we think we get to know him, he throws us a curve ball.

Should we expect him to continue to be a problem for our heroes then?

Kitsis: I think the best part about Rumple is we don’t know what he’s going to be. He’s either going to help us or hurt us, and at this point, we don’t know.

Emma's looking a little rough there at the end. Is she going to be okay or a bit of an emotional mess?

Kitsis: I think, right now, Emma is determined to find Hook. When she declared last night to Hook, "I will find you. I will always find you," she meant it. She’s going to go through a whole bunch of emotions.

Horowitz: She’s a very strong woman, and I think that she’ll be able to draw on that strength to help her face whatever she needs to face now, in a place that is going to be quite challenging.

Will any of the new characters from this season still be around for the second half?

Kitsis: We’re going to see Merida again, and the Camelot people are still there. But the main focus is obviously going to be on our core characters, which it usually is.

What themes do you intend to explore in the second half of the season?

Kitsis: Well, one theme is going to be about your past coming back to haunt you. And I think it’s going to be a lot about emotional closure.

Once Upon a Time returns on Sunday, March 6, 2016.