Season 4 of Once Upon a Time (OUAT) will see the introduction of Disney's Frozen characters, none of whom will be recognized by Henry Mills.  (Spoiler Alert!)

On Friday, Aug. 15, OUAT creator Adam Horrowitz told TVLine that Season 4 takes place in "the early part of 2013." Hence, Frozen has not shown up in theaters in the Once Upon a Time universe. In real life, the Disney animated-feature was released in November 2013. 

Hence, Frozen will not appear in Henry's magical book, which tells the true story of every fairytale character in existence. Instead, Henry will be blind to the show's newer arrivals -- Queen Elsa, Anna, Kristoff, Hans, and Pabbie the Troll King.

The Dark One, Rumpelstiltskin, considers Queen Elsa incomprehensible. So, he simply traps her in an urn back at his home in the Enchanted Forest. In the Season 3 finale, Emma Swan and Captain Hook accidentally bring the urn to Storybrooke, where Elsa is released. Recently, ABC network confirmed that Frozen's Arendelle will feature prominently in flashback sequences, which will explore "why Elsa became a prisoner of Rumplestiltskin."

The consequences of Elsa's arrival will be explored in the eleven-episode arc in the first half of Season 4. It remains unclear whether Elsa has family-ties with any of the Storybrooke characters. Certainly, Once Upon a Time showrunners have refused to divulge information.

"We will go on record as saying that we are not going to reveal that, for example, Elsa is somebody's sister," Horowitz said.

Indeed, Once Upon a Time has a very bizarre and complex family tree. In previous seasons, it was revealed that Rumpelstiltskin sired Henry's father, Neal. Snow White and Prince Charming give birth to Emma. Henry is Neal and Emma's lovechild. At birth, Henry is put up for adoption, and Regina becomes his foster-mom. Meanwhile, Regina is also Snow White's stepmother.

Feeling guilty about not raising Emma, Snow White and Prince Charming decide to have another child. The couple gives birth to a son, whom they name after the deceased Neal. In short, the main heroes and villains are family. Even the Wicked Witch of the West is Regina's half-sister.

Once Upon a Time Season 4 is coming to ABC on Thursday, Sept. 28 at 8/7c.