“Once Upon a Time” co-creator Adam Horowitz is ready to “let it go.” The executive producer and writer for the hit ABC show sent fans into frenzy when he tweeted a behind-the-scenes photo from Season 4.

“Casting for #OnceUponATime Season 4!” Horowitz posted. “Hard at work! Hope to see ya this fall!”

The photo that accompanied Horowitz’s tweet didn’t feature any cast members or a look at the set, but it did tease that viewers can definitely look forward to seeing “Frozen’s” Anna come to life on the small screen.

Casting for #OnceUponATime season 4! Hard at work! Hope to see ya this fall! pic.twitter.com/Zk5TWfAZnx — Adam Horowitz (@AdamHorowitzLA) June 13, 2014

“Role of Anna,” a printed sign taped to a wall or door reads. “Scenes 1 & 2 only.”

“Once Upon a Time” fans got their first taste of “Frozen” during the Season 3 finale. In the final moments of the episode it was revealed that Hook and Emma accidentally brought a stowaway (besides Maid Marian) back from the Enchanted Forest of the past. An urn from Rumplestiltskin’s dungeons poured out into the unsuspecting town, forming into the blue-clad “Frozen” Snow Queen, Elsa.

So, if Elsa was introduced in the finale -- who is Anna?

For those unfamiliar with Disney’s latest hit, “Frozen,” Anna is the Princess of Arendelle, and the younger sister of Elsa. After accidentally sending Arendelle into an “eternal winter,” Elsa exiles herself from the kingdom. It becomes up to Anna to not only save the kingdom, but reunite with her sister and return her to the family.

Anna and Elsa are not the only “Frozen” characters to be headed to Storybrooke in Season 4 of “Once Upon a Time.” The show is also looking to cast Kristoff, an ice merchant who assists Anna in finding Elsa.

According to TV Line, Elsa will be featured in approximately nine episodes in the coming season. Meanwhile, Anna and Kristoff will appear in “a bit less.”

Are you excited to see “Frozen” come to life on “Once Upon a Time”? What are your casting dreams for Anna, Elsa and Kristoff? Tweet your thoughts to @AmandaTVScoop.