Why 'Frozen' Was So Successful. 

Frozen at Christmas: The secrets of Disney's biggest hit UNLOCKED and how Let It Go 'changed the movie'

Behold the reasons why your child/niece/nephew/brother/sister LOVES this powerful story of sisters Anna and Elsa

Channel 4\'s Frozen at Christmas is an interesting, in-depth look at the incredible story of Disney\'s Frozen.

The movie about sisters Anna and Elsa, whose icy powers have trapped the kingdom of Arendelle in eternal winter, went on to become the most successful animated film of all time.

In the documentary, viewers hear from film-makers, performers, critics and fans who unveil the secrets of the film\'s success.

Frozen started back in 2011. Co-directors Chris Buck - from Tarzan fame - and Jennifer Lee (Wreck-It Ralph) hand picked 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 two sisters.

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

"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."

Even Disney admit they \'weren\'t ready\'

Frozen at Christmas reveals that not even Disney knew Frozen would be so big.

When it came time to merchandising the movie they were behind the huge demand.

Stores around the world had to try their best to keep up with demand. The likes of Hamleys even had to reduce shoppers to two Elsa dolls per customer.

You\'re not a hit until you have your own flashmobs dedicated to you..

* Frozen at Christmas aired on Christmas Day at 9pm it also airs tonight New Year\'s Eve at 8pm on Channel 4

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