Just when you thought you’ve seen every important Porsche hitting the surface, another one comes out and makes your jaw drop on the floor.

This example of a 911 Carrera RS 2.7 is the second car Porsche built and one of the four such prototypes so it’s rather special. In total Porsche built nine 911 Carrera RS for testing and pre-production purposes and this is chassis no. 9113600012.

The production date is still debated but it’s believed that the car was produced in April 1972, six months before the launch of the regular production of the model.

The biggest difference between this prototype and the production version is of course the lack of the iconic duck-tail rear spoiler. The first four prototypes of the Carrera RS were based on 911 S bodyshells that were modified to what would later become the 1973 Carrera RS spec.

Other differences include an 85-liter fuel tank, the chrome trim around the turn signals and an engine bay that was spray-painted black.

The same car, which is finished in Signal Yellow, appeared on a sales brochure for the 1973 model year, alongside three other 911s. Porsche also reportedly used it for rides with journalists. It was only after production of the 2.7 RS had ended that Porsche gave it for free to its first owner, a racing driver named Helmuth Koinigg.

The car changed many hands since then, including one stint in the U.S. where it was restored, and is currently at the hands of a German collector.

If you were looking for your next special Porsche or more specifically the second Porsche 911 RS ever made, bring you A-game at RM’s Porsche 70th Anniversary Auction and prepare for a bid war. The estimate is $1,250,000 to $1,500,000.