Mexican Filmmaker Alfonso Cuaron, whose film credits include Harry Potter and the Prisoner of Azkaban, Children of Men and Y Tu Mama Tambien, is set to release his latest sci-fi feature, Gravity, this August. Before Sandra Bullock and George Clooney made the final cast for the film, Scarlett Johansson, Natalie Portman, Angelina Jolie and Robert Downey Jr. were attached to the project.

In a panel interview with Cuaron at this year's San Diego Comic Con, the director candidly talked about why the Iron Man actor was replaced by Clooney.

Cuaron took four and a half years to helm the project and confirmed that Downey was indeed supposed to star in Gravity. However, the film kept on extending its process and "it was not the most compatible thing for what Robert is the best at. That is, he takes one scene and he just starts riffing," he said.

The director explains that the technology his team used requires preprogramming the film before shooting. It requires a great deal of preparation, something that Cuaron feels Clooney and Bullock are prepared to do.

Cuaron stated, "We animated the whole film before. We could have released an animated version with the voices of Sandra Bullock and George Clooney. We watched it and we gave suggestions and if they had notes or ideas, then it was just about programming the whole thing. it was amazing because, yes, they changed quite a lot, relatively speaking. But it was always in the context of what was there already."

Gravity tells the story of two astronauts stranded in space after their shuttle was destroyed by space debris. Bullock plays Dr. Ryan Stone, a medical engineer who is on her first Space Shuttle mission. He is joined by astronaut Matt Kowalsky, played by George Clooney.

Gravity will have its world premiere at the Venice Film Festival on August 28th and hits Australian theatres on October 3rd.

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Sandra Bullock Floats in A Space Shuttle: New Image Released from Alfonso Cuaron's Gravity [PHOTO]

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