This One-Off 1951 Cadillac Was Built for a Future Queen, and It's Heading to Barrett-JacksonA black 1951 Cadillac Series 62 convertible with a history unlike almost anything else on the market is crossing the block at no reserve, and Barrett-Jackson's listing for the car reads more like a royal biography than a typical auction docket. Before she was ever crowned Queen Elizabeth II, Princess Elizabeth toured Canada in 1951, and General Motors of Canada built this one-off Cadillac specifically so she could be seen, and see the crowds, during that royal visit.Cadillac built the car in-house at its factory, then handed it off to an aviation manufacturer to fit a custom clear bubbletop, an enclosure that kept its royal occupant dry without hiding her from onlookers lining the parade route. Under that glass sits the division's 331-cubic-inch OHV V8, paired with a heavy-duty four-speed Hydramatic automatic and, notably, a factory four-barrel carburetor, a setup used on only one other 1951 Cadillac. Cadillac also fitted power steering, power windows, power-adjustable front seats and an oversized radiator to keep the engine cool while creeping through parade traffic. The black exterior wraps around a red Hydes leather interior, and the dash still wears its original commemorative plaque noting the car's royal service.The provenance package is what separates this Cadillac from any other Series 62 convertible you'll find for sale. The consignor is including the original build invoice, period books and photographs showing the princess with the car, and a rhinestone replica of the George IV State Diadem, the crown later associated with Queen Elizabeth II throughout her reign. The car has since been treated to a full restoration finished to show-quality standards, and it remains a one-off; Cadillac never built another like it. For a deeper look at how the marque's postwar flagship evolved over the following decades, our research team's breakdown of the 1976 Cadillac DeVille traces that lineage.AdvertisementAdvertisementSo what does a car like this actually sell for? There's no clean answer, because nothing directly comparable has ever come up for sale. Hagerty Valuation Tools prices a standard 1951 Cadillac Series 62 convertible at roughly $58,200 in #3 (Good) condition, with #2 (Excellent) and #1 (Concours) examples commanding considerably more. That figure is a useful baseline for what a well-kept, ordinarily-optioned example is worth today, but it's just a starting point here. Once you factor in the one-off coachwork, the factory-installed second four-barrel setup, and a documented connection to a monarch who reigned for seven decades, this Cadillac is priced by history as much as by horsepower. It's the same dynamic we've seen play out with other provenance-heavy cars that hit the market carrying real Hagerty data behind them, from pace car Corvettes to low-production homologation specials, where the price guide sets the floor and the story sets the ceiling.The royal Cadillac is part of the docket for Barrett-Jackson's 2026 Las Vegas sale, which follows a run of strong results for the auction house this year, including a record-setting debut at its first Columbus sale. With no reserve attached, this parade car is guaranteed to find a new owner, whoever is willing to pay for a piece of the Queen's own motoring history.⚡️ Read the full article on MotoriousSign up for the Motorious Newsletter. For the latest news, follow us on Facebook, Twitter, and Instagram.