The news from BMW keeps on coming, with today’s tidbit centering on a lightweight ‘CSL’ version of the outgoing M6 Coupe that was fully developed by the automaker’s hallowed M division but never brought to life.

If you’re unfamiliar with the famous lettering, CSL stands for Coupe, Sport, Lightweight and marks the purest driver and most track-focused cars offered by BMW. The last model the CSL lettering was attached to was the E46 M3 Coupe, with the cars built in a limited run of just 1,400 units between 2002 and 2004--such tiny numbers make it an exclusive offering, and only the most dedicated opt for the extra expense and somewhat harsher and noisier ride characteristics of the car. 

It turns out BMW had also planned an M6 CSL, a car destined to be the most expensive in the automaker’s lineup, and even set about building a prototype. Though with the financial crisis of the recent past, the business case for such a high-end model just didn’t make sense and thus production was never given the green light.

The prototype featured extensive weight saving in its construction, with engineers managing to shed some 220 pounds from its curb weight. It also came with an active aerodynamics package, mostly under its floor, as well as an uprated V-10 engine.

Sadly, we may never know how the M6 CSL would have performed on the track, and with BMW’s greener focus of late the chances of such a car being produce grow slimmer with each passing day.

Other BMW M cars that reached the prototype stage but were never built include a rear-wheel drive version of the first-generation X5 SUV, as well as this M8 supercar whose V-12 engine would go on to power one of the greatest supercars of all time, the McLaren F1.

Perhaps the closest we’ll ever get is the limited edition M6 Competition (pictured), which came with some minor suspension upgrades.