American Shelby has built numerous versions of the Cobra sports car over the years, though among the most desirable—and collectible—are the 427 S/C and Competition cars.

One of those cars, a 1965 Shelby 427 Competition Cobra, is now headed to auction and is likely to fetch millions.

The car, which bears chassis number CSX3006 and features its original aluminum body, is one of just 23 examples in existence, and it's set to go under the hammer at the Mecum auction next month in Kissimmee, Florida.

The 427 S/C and Competition cars were born out of an international racing program in the mid-1960s. For homologation, Shelby needed a minimum of 100 of the 7.0-liter V-8 race cars, but the company only got around to building 56, including two prototypes. Without those extra cars, Shelby had to can the racing program.

1965 Shelby 427 Competition Cobra bearing chassis no. CSX3006 - Photo credit: Mecum

1965 Shelby 427 Competition Cobra bearing chassis no. CSX3006 - Photo credit: Mecum

Shelby proceeded to adapt the race cars for use on the street. The company undertook this modification for 31 vehicles, labeling them as Semi-Competition cars with the S/C designation. Meanwhile, 23 cars retained their race car configurations and were labeled the Competition cars, like the one shown here.

The Competition cars were sold to privateer racers. Chassis no. CSX3006 was originally ordered by William Freeman of Muncie, Indiana. He took delivery in 1965 and entered the car that year in two SCCA races. After receiving a contract to race with a team in Europe, he offloaded the Shelby to a U.S. Air Force officer stationed in France. The car was then sold in 1966 to British racing team The Chequered Flag.

It was during this time that three Formula 1 drivers—Chris Irwin, David Piper, and Bob Bondurant—all took turns behind the wheel. Among its racing appearances, the most notable was the 1966 Ilford Films 500 at Brands Hatch, where Piper and Bondurant drove it to victory.

Now it is seeking a new owner. The car is lot number F231.1 for Mecum's Kissimmee auction, which runs Jan. 2-14.