It's called saving the best for last. Porsche, for example, does this towards the end of the current generation 911's lifecycle with the GT2 RS. Its fellow German rival, Mercedes-AMG, is doing its best to emulate the 911's success with its own high-performance sports car, the AMG GT. Believe it or not, the AMG GT launched for 2015 and in today's ultra-competitive market, a replacement will soon arrive. Until that happens, the folks at Affalterbach continue to be busy prepping the ultimate AMG GT, the Black Series.

Our spy photographers were hanging out at the Nurburgring earlier this week because testing season is on. General weather and track conditions are ideal. Mercedes-AMG test engineers didn't let a good weather opportunity go to waste and the camouflaged vehicle you're looking at is the track-focused but fully street-legal AMG GT Black Series.

How do we know for sure it's the Black Series? For starters, take note of the prototype's aero pack, which includes a revised front bumper and a more aggressive splitter. Interestingly, this prototype's exhaust pipes do not look production-ready. Lastly, the rear wing is more aggressive. You'll see the differences if you were to compare this prototype to the just on sale AMG GT R Pro.

For now, that is the most hardcore AMG GT you can buy and for many, it's more than enough power and performance. But the upcoming Black Series will add that extra bit of craziness only the most hardcore enthusiasts can handle and are willing to pay extra for.

The AMG GT Black Series will come powered by the same 4.0-liter twin-turbo V8 found in theGT R Pro, only with more power. Our sources tell us anywhere from 650 to 700 hp is possible. The Mercedes-AMG GT 63 S 4-Door, for example, has 630 hp on tap. Along with reducing weight wherever possible, the GT Black Series will be the most hardcore Mercedes-AMG to date, with one exception: the Mercedes-AMG One hypercar. Expect the Mercedes-AMG GT Black Series to debut sometime in 2020. Its price will be very high and the build count extremely low.