Once Upon a Time
Once Upon a TimeFacebook/Screenshot

When "Once Upon a Time" returns this fall, fans of the fairytale drama will be introduced to three new characters – Elsa, Anna and Kristoff from Disney's "Frozen" – and rumors swirling around suggest that the Queen of Arendelle might be cast as an evil character.

Elsa, who has the power to freeze anything that comes in her path, is believed to be the villain for the first half of the next season. While nothing much is known about the plot, reports have it that Elsa will appear in nine episodes, while Anna and Kristoff will be in as many as six.

In "Once Upon a Time," Kristoff will be moving with Anna to the castle, and this move is going to be tough for her beau, according to a TVLine report.

Despite "Frozen" characters making an appearance in the season, the co-creators of the series, Eddy Kitsis and Adam Horowitz, revealed that they have no plans to set the entire season four in another realm.

"I don't want to say anything definitive, but we are not looking to in, like episode 3, go, 'Oh my God, we're not on Mars,'" joked Kitsis, according to Entertainment Weekly. "As always on the show, we like to show you different worlds. I would be let down if we don't get to see Arendelle," he added.

Spoilers surrounding season four indicate that the relationship between Emma and Regina is going to worsen. Emma has essentially destroyed Regina's relationship with Robin Hood and now that she is starting a romance of her own. 

"Here's the thing," explained Horowitz about what Regina will be like in the next season. "What we feel like we've done with Regina over three years is grown the character. She has changed and evolved, and this doesn't change that.

"What it does is it changes the way she reacts to this. That's the drama for us — how does this "new" Regina deal with this kind of adversity? We're throwing a challenge in her way. This is not about her suddenly becoming that character we met three years ago," he told TVLine.

The upcoming season will also deal with the story of how Robin Hood lost his wife. While season two saw Marian ill, she was later cured and even gave birth to Roland. But season three had Robin Hood talking about losing his wife, but not due to any illness.

"So something clearly happened that we'll explore next season, where they were separated and she died — and he certainly didn't think the Evil Queen killed her. There's a story there to be told," Horowitz told TVLine.

"Once Upon a Time" Season airs Sundays at 8 p.m. EDT this fall on ABC.