BMW's legendary series of art cars, painted by the likes of Roy Lichtenstein, Andy Warhol, Robert Rauschenberg and David Hockney beginning in 1975, are well known to auto enthusiasts.

In addition to the 17 official examples however there is one car that was commissioned by a private client, a 1979 BMW M1 Pro Car painted by Frank Stella. Stella created the second in the official Art Car series in 1976 when he painted a 3.0 CSL. The M1 was commissioned by seven-time world champion IMSA racer Peter Gregg, who asked Stella to base the design on the famed artist's "Polar Coordinates" series.

The M1 appeared in the official art car lineup that same year, painted by Warhol. The Stella M1 was donated to the prestigious Guggenheim Museum in 1999, which has now decided to de-accession it. The car will be offered during UK auction house Bonhams' collector's motorcars sale at Quail Lodge in Carmel, California on August 18-19.

It is expected to fetch in excess of $500,000. Given that this is the only BMW car ever painted by an authorized BMW Art Car artist outside the official 17, it could easily go for twice that amount.