"We're going to learn a whole new side to 'Frozen' that we haven't seen before. We pick up where the movie ended," said actress Lana Parrilla, who plays the Evil Queen on the show.
The cast of characters who've made the fictional city of Storybrooke their home for the past three TV seasons were quick to warm up to the crossover idea.
"There was a reason so many people watched 'Frozen' in the first place,"said actress Jennifer Morrison, who plays the daughter of Snow White and Prince Charming. "There are those messages of being misunderstood, needing to find a way to be the best version of yourself and it's really nice to have those themes pulled in through 'Frozen' characters."
While the "Frozen" storyline will impact most of the characters on the show, the ice princesses will not completely take over.
"We've brought them in in our own way. They're inspired by 'Frozen.' They're not walking directly from the animated feature, but I feel that we're faithful to them in a way that the fans will be happy," actress Ginnifer Goodwin said.
The show's stars can promise fans they'll get the same type of fairy tale fun they've become accustomed to seeing.
"Hope is always a universal theme and that's what drives our story and that's what drives people to watch it," said actor Josh Dallas also known as Prince Charming.
"Once Upon a Time" premieres Sunday at 8 p.m.