And the characters couldn't be more different – the kindly Pabbie the Troll King, and Anna's scheming would-be suitor Prince Hans.
John Rhys-Davies, who played the dwarf Gimli in the Lord of the Rings trilogy, will play Pabbie, whose healing powers helped Anna in the movie. And Tyler Jacob Moore, who plays Tony Markovich on Showtime's Shameless, will play Hans, the good prince turned bad prince from the Southern Isles.
ABC's decision to introduce Frozen characters into Once Upon a Time's fairy-tale universe has fans of both the show and the movie buzzing. ABC showed the first clip from the crossover at Comic-Con this weekend – a scene from Once's upcoming Season 4 premiere showing Anna (Elizabeth Lail) and Elsa (Georgina Haig) putting flowers on their parents' gravestones.
Elsa also pops up at the end of the season's new trailer, emerging from a puddle of water and flinging off her gloves before strutting out of the frame.
"Awake, arise or be forever frozen," the narrator intones.
Also, Scott Michael Foster has been cast as the hunky ice picker Kristoff.
The Frozen story line on Once Upon a Time will take place after the events depicted in Disney's Oscar-winning film.
Disney / Everett; Getty