Georgina Haig plays Queen Elsa and Elizabeth Lail is Princess Anna in Once Upon A Time.
The snow queen, played by Georgina Haig, was seen arriving into Storybrooke after emerging from Rumplestiltskin's vault in the season three finale and will be joined by sister Anna (Elizabeth Lail), Kristoff (Scott Michael Foster) and even his reindeer Sven.
Some say "sell-out" but for the series' showrunners and self-confessed Disney addicts Eddie Kitsis and Adam Horowitz, the film became such a hot topic in their writers' room that merging Arendelle with Storybrooke became a natural move.
"We had seen the movie, fell in love with it then all our writers saw it and loved it," says Horowitz. "We were super-inspired and started to get ideas, so we called Disney and asked, 'Can we do this?'"
"It was born out of us wanting to do expensive fan fiction," adds Kitsis. "But trust me - Disney does not take their most successful franchise and say: 'Hey, will you throw it on a show right away?' They protect it and are very beloved over it, but we had a passion for it and are fortunate that they trust us to do it."
So what can viewers expect when the two fairy tale worlds collide? Producers are quick to point out that the story arc is not a sequel to the film - rather they will explore the characters' back-stories and how they relate to the Once favourites.
While Anna prepares for her wedding to Kristoff, viewers will find out how Elsa ended up in the vault of Rumplestiltskin, his alter-ego Robert Carlyle saying he doesn't yet know the full story, "but I imagine it's not going to be good".
While she is expected to spark a power battle with the Evil Queen/Regina, Elsa may find a friend in Emma, played by Jennifer Morrison.
The similarities between Elsa and Emma were a major motivation for Once producers to explore the Frozen world and Morrison says she hopes the relationship between the two will finally give Emma "more reasons to smile".
"Elsa is someone she's very intrigued by because she doesn't have control over magic the same way Emma doesn't have control over her magic and it's not something either of them asked for.
"She's been through so much and been forced to grow over the last three years, so I'm always looking for the moments that are lighter in the midst of the crises she's dealing with all the time.
"The [Frozen] characters have been such a wonderful addition. It already feels like they've always been there, so there is something really effortless about the way they've been woven into the storytelling."
Television preview
What: Once Upon a Time meets Frozen
Where and when: TVNZ Ondemand, from Tuesday.
