The hit ABC series Once Upon a Time held their annual Comic-Con panel earlier today in Ballroom 20, where fans were given their first look at a scene featuring Frozen characters Anna (Elizabeth Lail) and Elsa (Georgina Haig). While that footage isn't online quite yet, series creators Edward Kitsis and Adam Horowitz also showed a parody video, where they revealed their "inspirations" in bringing the hit Disney movie Frozen into the ABC series. Take a look at the video that was shown at the panel earlier today, then read on for more details about new and returning characters for Season 4. We also have photos from the official Twitter account featuring the cast members and producers on the panel.

RELATED: Labyrinth Mini Epics Figures Unveiled by Weta Workshop

The Once Upon a Time Season 3 finale in May ended with a glimpse of Elsa emerging from Rumpelstiltskin's vault. Both Elsa (Georgina Haig) and her sister Anna (Elizabeth Lail) were cast shortly thereafter, with the producers bringing along the first clip from Season 4 that features the sisters putting flowers on their mother's tombstone, where Elsa tells her sister, "Anna, they would be so proud of you." Elsa goes on to tell Anna that she has a surprise in store for her upcoming wedding. Anna's beau Kristoff will be played by Scott Michael Foster.

The producers also released a second clip which revealed the return of Giancarlo Esposito as the Mirror, who hasn't been on the show since December. The scene featured Regina (Lana Parrilla) visits a holding cell in the hospital and demands that the Mirror be returned to her, when she asks a favor of her old friend, who has been bloodied and beaten. Here's what she told the Mirror in the clip, which won't be released anywhere else.

"There's somebody standing in the way of happiness. I need your help getting rid of them."

One of the secrets that wasn't revealed in Ballroom 20 was which character Elizabeth Mitchell is playing. We reported that she joined the cast earlier this month as a character who has ties to both Storybrooke and the Frozen setting of Arendelle.

Once Upon a Time returns with its Season 4 Premiere on Sunday, September 28 at 8 PM ET on ABC.