Frozen at Christmas (2014)

Frozen started back in 2011. Co-directors Chris Buck - from Tarzan fame - and Jennifer Lee (Wreck-It Ralph) handpicked Kristien Bell (Anna), Idina Menzel (Elsa), Josh Gad (Olaf), Jonathan Groff (Kristoff) and a cast that was perfect for the movie.

"Because there were cameras [when we shot the movie], in my first session I was so nervous," says Bell in the programme.

"Once they had done their bits, I could easily build on it," adds director Lee.

"It was so much fun working with Kristian," says Broadway star, Idina Menzel.

Frozen is based on Hans Christian Andersen The Snow Queen.

"The snow queen character intrigued me," says Buck. "I always thought it would make a good musical."

In Frozen, fearless optimist Anna teams up with rugged mountain man Kristoff and his loyal reindeer Sven in an epic journey, encountering Everest-like conditions, mystical trolls and a hilarious snowman named Olaf in a race to find Anna's sister Elsa.

The film investigated a different kind of love. The love between the two sisters.

"This is something that is quite new," they add.

According to the writers, Let It Go, 'changed the whole movie'.

"Let It Go changed the course of the story," says songwriter Robert Lopez.

"There is that moment when Elsa is at the top of a mountain and she is fleeing from everything and that is where her powers come out. It captures the feeling of 'screw my family'," adds Kristen Anderson-Lopez.

"Once I heard it I had to change the whole movie," adds Lee.

Book of Mormon comedian Josh Gad was "perfect" for the role of Summer loving Olaf, say the writers.

Olaf adds the comical edge that "really makes the movie," it is said. "That is where the comedy came from."

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