Classic Shelby automobiles are among some of the most sought-after collector cars on the planet. These cars were only priced at a few thousand dollars when new, though today a clean example can easily fetch a quarter-million dollars or more. And if you happen to own a rare Shelby, or even better, a one-of-one, then the value can easily reach into the million-dollar range.

While not quite a million-dollar car the last time it sold, this one-of-one 1967 Shelby GT500 convertible is quite unique, and will be making a rare public appearance this summer at the Concours d’Elegance Texas, reports Hemmings Auto Blog.

Built in 1966 as a ‘67 model, this Shelby GT500 droptop was the only ‘67 convertible to receive dual carburetors from the factory on the 428 cubic-inch Police Interceptor engine. Initially used as a company car and engineering prototype, it was later converted over to 1968 sheetmetal to be used as a marketing tool for the upcoming ‘68 GT500 convertible, before being sent back to Ford for processing.

The car then traded hands for the next decade, with its owners never quite certain of the prize they had. It wasn’t until 2003 that Shelby American authenticated the car, and in 2009 it sold for $850,000 at auction, making it one of the world’s most valuable Mustangs.

It will join the one-of-one Dragonsnake at this year’s Concours d’Elegance Texas, putting two exclusive classic Shelby supercars at one event. If you live in Texas and love Mustangs, this is one event you have to try and attend; who knows when you might see these two rare cars ever again?