It's been almost four years since the world fell in love with

Frozen

, one of the most successful animated films of all time.

In the story, fearless princess Anna sets off on a journey alongside a rugged iceman, his pet reindeer and a snowman to find her sister Elsa, who has accidentally trapped their kingdom in eternal winter thanks to her strange icy power.

But it's now been revealed that's not exactly how the story was supposed to go.

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Frozen's Anna and Elsa. Photo / Supplied
Frozen's Anna and Elsa. Photo / Supplied

In an interview with

Entertainment Weekly,

producer Peter Del Vecho finally lifted the lid on the original script - and boy, does it change things.

"So when we started off, Anna and Elsa were not sisters. They weren't even royal," he said.

Instead, Elsa was a full-blown villain because she had been stood up at the altar on her wedding day, and chose to freeze her own heart - leading viewers to believe she's the one in the prophecy destined to ruin Arendelle.

"We started out with an evil female villain and an innocent female heroine and the ending involved a big epic battle with snow monsters that Elsa had created as her army," Del Vecho explained.

He added that in response, Prince Hans would create an avalanche to destroy the city, and Anna convinces Elsa to save everyone. Elsa suddenly realises she's not the subject of the prophecy - Prince Hans is - and her heart unfreezes.

But that storyline just wasn't working.

"The problem was that we felt like we had seen it before," Del Vecho said.

"It wasn't satisfying. We had no emotional connection to Elsa - we didn't care about her because she had spent the whole movie being the villain. We weren't drawn in. The characters weren't relatable."

Eventually, the movie's creators transformed the script into good versus fear, instead of good versus evil - and Del Vecho knew they'd nailed it.

"When the final piece of the creative puzzle fell into place, that moment was downright, well ... heart warming."