Frozen isn't just coming to Once Upon a Time Season 4.
It's coming to ABC as a whole.
The network announced via press release today that it will air “The Story of Frozen: Making a Disney Animated Classic” on Tuesday, September 2 at 8/7c.
The one-hour program will chronicle the origins/evolution of this Disney smash, including interviews with the creative team and comments from Kristen Bell (Anna) and Idina Menzel (Elsa).
The special also teases "exciting announcements about the next chapter of Frozen," along with a preview of the film’s characters - Anna, Elsa and Kristoff - in their upcoming appearance on Once Upon a Time.
Speaking of which, here's a look at those characters, courtesy of Once Upon a Time Season 4, Episode 1 ("A Tale of Two Sisters"):