The Mercedes-Benz CLS ignited the four-door coupe market when it was first introduced back in 2004, and since then we’ve seen several other luxury rivals attempt to emulate the design with cars like the 2010 Porsche Panamera, recently revealed 2010 Aston Martin Rapide and upcoming Audi A7.

Now, prototypes for Mercedes’ next-generation CLS has been spotted, revealing a few subtle clues about the new model. The new car is expected to be launched in late 2010 as a 2011 model and positioned more upmarket to bring it in line with some of its more premium rivals. This will also allow Mercedes-Benz to introduce a second four-door coupe model, rumored to be based on its next-generation small car platform.

The new design will feature a wider track, as indicated by the extended wheel arches seen on previous test mules, and according to insiders its platform is borrowed from the current S-Class sedan flagship. The latest computer-generated rendering is an accurate representation of what the new car will look like.

New to the CLS will be a hybrid option based on the same powertrain as the one used in the recently revealed S400 BlueHybrid. Other engine options will include both V-6 and V-8 powerplants, and there will be a high-performance AMG model, which you can see spy shots of by clicking here.

Also rumoured to be in the works is a new ‘shooting brake’ variant, which you can read about by clicking here.