Board Thread:Spoilers!/@comment-2153169-20140908192157/@comment-24674051-20141009165616

I think that the way I read that is that anything that is truly considered as canon from Frozen is set, and won't be twisted. So the fact that the King and Queen RAISED Anna and Elsa can not be changed. But, there was nothing ever definitive said about whether the King and Queen were the Natural Parents or not.

Try this twist on. Once Upon a Time, there was a King and Queen in Arendelle. When they were young, they were told that they could never have children. This greatly saddened the royal family. So they secretly set out and found a child that they could adopt (in Mist Haven), and once they adopted her, she (it was Elsa) became the heir apparent to the throne. To prevent any issues regarding the succession of the throne, the King and Queen kept the adoption secret. Of course, the King and Queen knew nothing about the baby's background when they adopted her, so the manifestation of the ice powers came as quite a surprise.

Then, a couple of years later, through some (undefined) set of miraculous circumstances, the Queen did become pregnant, and Anna was born. The fact of the adoption remained secret, even from the girls, and both girls were raised as sisters, and had the typical fun relationship until the accident (documented in Frozen). For all intents and purposes, as far as anyone else was concerned, both girls were of the royal family, and Elsa was next in line. The only people that knew otherwise were The King, The Queen, and the mystery person that helped to procure the child.

One day, as the children were growing, the King and Queen became more and more concerned about Elsa and her ever increasing and uncontrolable powers. Because no one in Arendelle knew of the adoption, or that Elsa was from Mist Haven, they chose to secretly visit the mystery person in Mist Haven that helped them adopt Elsa. In order the keep the secret of the mission, they set out under the pretense of a diplomatic mission, and then altered course once they were at sea.

Unfortunately, the ship went down in a storm during the journey, and the King and Queen perished. The secret would have gone down with them, except for a hastily written note.