Two years ago the Mercedes 300 SLR ‘Uhlenhaut’ Coupe became the most valuable car in the world after being sold for €135m (£115m). Could the 500K surpass this?

It won’t be the only lot catching the eye as the auctions roll on. Another car that has been under wraps for decades is the late Klein’s 1955 Mercedes-Benz 300 SL ‘Alloy’ Gullwing. Just 29 were made, with this one being the only example finished in black – at one point it was owned by legendary US Ferrari importer Luigi Chinetti.

Also included is the last surviving Horch 855 Special Roadster, a 1939 car which was used in Hollywood publicity photographs in the 1950s, and a 1967 Iso Grifo A3/L Spider Prototype by Bertone which Klein bought off TV film producer Greg Garrison – known for creating The Dean Martin Show and directing one of the landmark 1960 presidential television debates between John F. Kennedy and Richard Nixon.

Many weren’t even sure this hallowed collection existed, but now RM Sotheby’s will oversee each car’s sale from October this year.

“Bringing something out of hiding that’s only been rumoured to exist, like the legendary Klein Collection, is truly special,” said Sotheby’s car specialist Cary Ahl.

“Discovering a hidden Mercedes 500K or an Alloy Gullwing is the kind of story that resonates with everyone, not just automotive enthusiasts. What Klein amassed here is one-of-a-kind, and we know that many of these cars will live on for generations, powering new projects, or preserved in their original state.”