A dusty looking green Ford Mustang with some surface rust and holes cut in the trunk could very well become the most valuable Mustang -- maybe even the most valuable American muscle car of any kind -- ever sold at auction.

The 1968 Mustang GT, which will be offered for sale by Mecum Auctions at an event in Kissimmee, Florida, on Friday, was driven by the actor Steve McQueen in the movie Bullitt.

Even if you've never seen the movie in its entirety, there's a good chance you've seen clips from its famous chase scene. It features the Highland Green Mustang with black wheels and McQueen clearly in the driver's seat in many shots. And there have been plenty of movie chase scenes done since that were influenced by the Bullitt chase, considered the first and still one of the best "modern" auto chase scenes. There were car chases in movies before but they looked very different.

The current record price for a Ford Mustang sold at auction is $2.2 million paid for a 1967 Shelby GT500 at Mecum's Kissimmee auction last year. The highest price ever paid for any muscle car at auction was $3.5 million for a '71 Hemi 'Cuda convertible sold at a Mecum auction in Seattle in 2014. This car could fetch more than either of those cars.

This Mustang's uniqueness makes it difficult to predict the ultimate selling price. Ordinarily, past association with a celebrity and even appearance in a movie don't add significantly to a car's value. They just make for cute stories to tell when showing off an old car to friends. It's usually the car itself, its desirability and its rarity, that contribute most to its value.

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