2013 Mercedes-Benz S-Class Spy Shots

Mercedes-Benz only took the wraps off its facelifted S-Class range in 2009 but development on the next-generation of the flagship sedan is well underway as revealed by this latest prototype, captured by photographers as it was undergoing high-speed testing on the Nurburgring race track in Germany.

Under the quilted camouflage, the images reveal the new LED daytime running lights and indicators, which on the new model appear to be at the top of the headlight.

Due for a reveal in late 2012 as a 2013 model, the new S-Class is expected to be slightly longer than the current model and come packed with a range of fuel efficient engines as well as a new plug-in hybrid option. The prototype seen here sports a slightly longer hood and wheelbase, suggesting the overall size of the S-Class will grow.

While it's still too early to confirm any details, R&D boss Dr. Thomas Weber has previously said that new direct injected and turbocharged engines will make up the powertrain lineup for the next S-Class, which means you can expect a similar lineup to the one in the 2011 Mercedes-Benz CL-Class.

The new S550 should come with a 429 horsepower twin-turbo V-8, while the S600 should pick up a new iteration of the automaker’s twin-turbo V-12 with around 510 horsepower on tap. The AMG model will get a twin-turbo 5.5-liter V-8 with around 550 horsepower.

Weber has also previously revealed that the plug-in hybrid powertrain from the 2009 Vision S500 Plug-In Hybrid Concept will also appear in the next-generation S-Class and promise sub-6.0 second runs to 62 mph and fuel economy of 70 mpg or better.

In terms of styling, expect influences from the fluid F800 Style concept car to feature on the new S-Class. Some advanced technology like the recently launched PRE-SCAN active suspension set-up and futuristic SERVO-HMI (Human Machine Interface) virtual operating assistant may make it too.