Back in January this year, the famous 1968 Ford Mustang GT350 driven by Steve McQueen in 'Bullitt' became the most expensive Ford Mustang to ever sell at auction, selling for a record-breaking $3.74 million. Just seven months later, the Bullitt Mustang's auction record has already been beaten.

Last weekend, a 1965 Ford Mustang Shelby GT350R prototype went under the hammer at the Mecum Indy 2020 auction, where it sold for a staggering $3.5 million. Taking auction fees into account, the final selling price was a whopping $3.85 million. That makes it the most valuable Ford Mustang in the world, beating the Bullitt Mustang.

Known as the "Flying Mustang," the 1965 Ford Mustang Shelby GT350R is arguably the most historically significant Mustang in the world, so we're not surprised that it set a new auction record.

Driven by British racing driver Ken Miles, who also helped develop the legendary Ford GT40, which was chronicled in the 'Ford v Ferrari' Hollywood film last year, this is the first Shelby GT350R ever built, the first Shelby Mustang competition car, and the first Shelby Mustang to win a race when it made its competition debut at Green Valley Raceway in 1965.

A famous photograph of the GT350R gaining air during the race earned it the nickname of the "Flying Mustang" and was used to promote the Mustang to change people's perception of the pony car.

As well as being the first competition Shelby Mustang, the GT350R was used as an engineering mule to test parts for the second team car and 34 customer R-models. It was also used as a demonstrator car for prospective buyers of the GT350R. In 1966, the first GT350R was sold for a mere $4,000 to a Ford Performance Division engineer, who had a racing-spec GT40 engine installed.

After changing owners over the years, the GT350R was meticulously restored back to its original 1965 specification. The restored car was presented at the 2014 Amelia Island Concours to celebrate the Mustang's 50th anniversary and won a Best in Class award. Chances are the GT350R prototype will retain its title of the world's most expensive Mustang for a very long time.