Actor Tom Cruise has been training for a stunt in the upcoming film 'Mission: Impossible 6' for a year, revealed producer David Ellison. "It's going to be... the most... unbelievable thing that Tom Cruise has done in a movie," added David. Earlier, Tom had filmed a stunt on top of the 2,717 feet tall Burj Khalifa, the world's tallest skyscraper.