As ABC's Once Upon a Time reaches its winter finale, the series will be testing some of the show's core relationships.

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Once Upon a Time co-creators Adam Horowitz and Edward Kitsis spoke with TVLine recently and previewed the upcoming midseason finale.

"Two of the show's most beloved relationships will be tested and changed forever as Storybrooke says goodbye to some of their own," Horowitz and Kitsis teased. "In the Enchanted Forest, things gets classically evil as we face off against an embarrassment of witches."

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Based on the way things are shaping up, one of those "tested" relationships could be Belle (Emilie de Ravin) and Rumplestiltskin (Robert Carlyle). Horowitz previously spoke with TVLine about Belle's role in the fall finale, revealing that she will be showing some heroism in the wake of Rumple's darkness.

Horowitz said that Belle's "strength and heroism play a key part in the fall finale" with Rumple becoming more and more bankrupt morally. There will also be a flashback in the episode to "another bit of her time in the dark castle with Rumple."

The other significant couple could be Emma (Jennifer Morrison) and Hook (Colin O'Donoghue), a coupling that is currently in peril with Rumple now wanting to kill the latter. Meanwhile, Emma is left unaware.

Once Upon a Time airs Sundays at 8 p.m. ET/PT on ABC.

Watch the promo for the next episode of Once Upon a Time here:

Tags: Once Upon A Time television ABC