'Monsters University' was "hard" to make.
The upcoming animated flick marks the first prequel produced by Pixar Animations - the Disney-owned studio behind the original 'Monsters, Inc.' and the 'Toy Story' movies - and producer Kori Rae admits it was a challenge to create an interesting storyline for the new movie as audiences are already familiar with loveable monsters Mike and Sulley.
She said: "One thing we learned for sure early on is that prequels are hard. They're definitely, definitely hard, because a lot more has to go into fear now. How to not make your film predictable. Everybody knows how it ends.
"Everybody kind of knows who the characters are at the end of the film. And you have to figure out twists and turns along the way to keep the audience engaged and involved and surprised, so that they're rooting for a character even though they know how it ends."
'Monsters University' sees Billy Crystal and John Goodman reprise their vocal roles as Mike and Sulley, while Dame Helen Mirren also joins the star-studded voice cast as university principal Dean Hardscrabble, and Rae says the actress was at the "top of our list".
She added to Collider.com: "As soon as we had the character designed and the story character description kind of nailed down, she was definitely at the top of our list - on Dan's list - creatively. An incredible talent that they hoped, at that time, that we could get. So it was a huge thing for us and she's just amazing."
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