Pixar’s 10th film was chosen to open the prestigious Cannes film festival today - which evokes the curious image of a bunch of sharp-suited/ballgowned people crowding into a cinema, slipping on 3D glasses and watching a cartoon.

But then, this is Pixar, and Up is much, much more than just another cartoon. Here's how it all happened...

1. Thank Wall-E.

Yes, Pixar’s little robot is actually responsible for both Monsters Inc. and Up. Why? Because co-writer/director Pete Docter actually worked on cracking the script for the film before deciding to leave it in the capable hands of Andrew Stanton. Twice.

For a while way back in 1995, Stanton and Docter worked together on developing Wall-E, then called Trash Planet, and focused on the droid plus the gel-like “aliens” that were originally planned to be the focus of the second act.

But Docter just couldn’t get a handle on what the film should be – leaving first to make Monsters, then revisiting an idea he’d had even before trying to crack Wall-E.

That idea? It was based around a sketch…

Next: It Began With Balloons