"When we first joined the project there was a script that was a live-action sort of Romancing the Stone kind of adventure," songwriter Kristen Anderson-Lopez tells PEOPLE about working on what would go on to become the Oscar-winning animated Disney film and the highest-grossing animated film of all time. It is now available on Blu-Ray/DVD.
Loosely based on Hans Christian Andersen's fairy tale The Snow Queen, Frozen had a long road to the big screen that included many rewrites and changes.
"We tried writing a couple of songs for that [original script] but it was sort of like tuna and chocolate. It just wasn't a script that was singing," says Anderson-Lopez. "But Disney wanted a musical, so we set a daily meeting from noon to 2 p.m. with the story team that lasted for two years."
Among the changes discussed were the true intentions of Idina Menzel's character, Elsa. This was a debate that was still going strong even as Anderson-Lopez and her husband, Robert Lopez, were tasked with writing what would become the film's breakout, Oscar-winning song "Let It Go."
"We were still like, 'Is she a villain? Is she not a villain?' All we knew was that Elsa's powers were going to come out and she was going to be chased up a mountain and transform into the Snow Queen," says Anderson-Lopez.
"We just put ourselves in the mindset of what it would feel like having to leave everything and everyone you know behind but getting the great release of letting go of your powers. Once the hook 'let it go' came out, we wrote it in about one-and-a-half days."
And the song changed the film forever.
"We wrote the song and sent it to [the movie's directors, Chris Buck and Jennifer Lee], and they said, 'We're going to have to rewrite the entire script,' " Anderson-Lopez says of "Let It Go," which has become the first Disney song to crack the top 10 on the Billboard Hot 100 since Vanessa Williams's "Colors of the Wind" from Pocahontas. "We are so grateful to them for doing that."
Courtesy Frozen Fever