While "CaptainSwan" shippers will undoubtedly want Emma (Jennifer Morrison) and Hook (Colin O'Donoghue) to continue their blossoming relationship on ABC's Once Upon a Time, it won't be an easy going for the couple.

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Once Upon a Time co-creators Adam Horowitz and Edward Kitsis spoke with TVGuide.com recently about the Emma-Hook relationship and how their happiness as a pairing may not sustain itself through Season 4.

"It's going to be tricky for the two of them," Horowitz revealed. "Just because we saw their feelings reach a new level at the end of last season doesn't mean that that's the end of the story."

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It seems that Emma's conflicting feelings might be what's holding them back from becoming stronger.

"Emma is obviously a person who has a tough time trusting people and letting her guard down," Kitsis said. "Sometimes you may feel something for somebody but your feelings hold you back."

Horowitz previously revealed to Entertainment Weekly that there would be more of Emma's past explored than ever before in Season 4.

"In the first half of the season, we're going to see more of Emma's past than I think we've seen in all the other previous seasons combined," Horowitz teased.

The characters will also have to deal with the latest threat to Storybrooke, Frozen's Queen Elsa (Georgina Haig) in the first part of the season.

Once Upon a Time Season 4 is set to debut Sunday, Sept. 28 at 8 p.m. ET/PT on ABC.

Watch the promo for the new season of Once Upon a Time here:

Tags: Once Upon A Time television ABC