The next-generation BMW 7-series has again been spotted testing in this latest set of spy photos.

Our spy photographers report seeing both regular and long-wheelbase versions of the 7-series testing with new bodywork. While previous test mules have worn more similar bodywork to the current 7-series, these prototypes appear to have significantly changed styling.

BMW is planning to take the fight to the new Mercedes S-class with the 7-series, which development boss Herbert Diess calls the most technically advanced car in BMW’s history. 

Due to launch in late 2015, the new car will receive its world debut at the Frankfurt show in autumn of that year. 

The new 7-series will ditch the traditional steel monocoque construction of today’s model for a structure that uses a mix of steel, aluminium and carbonfibre. Autocar has been told that this will cause the base 740i to undercut dramatically the 1900kg kerb weight of today’s model, and potentially even the 1670kg of the current entry-level 5-series. 

The plan to incorporate carbonfibre in load-bearing elements of the new 7-series comes after extensive research and development of the lightweight material during the creation of BMW’s new range of i models.

The reduction in weight for BMW’s flagship saloon will come about without any significant change in dimensions, if this early prototype is any indication. It is expected to be about 5010mm long, 1815mm wide and 1425mm tall. Two wheelbase lengths will be offered. 

Known internally under the codename G11, the new 7-series will once again come with the choice of six-cylinder, V8 and V12 petrol engines, as well as six-cylinder in-line diesel units. A petrol-electric plug-in hybrid version of the new 7-series is also planned. 

A further possibility is a new ZF-engineered nine-speed automatic gearbox as standard, although this is yet to be confirmed. Rear-wheel drive and all-wheel drive will be offered. 

In a bid to muscle in on the success of the Mercedes-Benz S63 AMG, BMW is also considering a new 760 xDrive M Performance model running a powered-up version of the company’s twin-turbocharged 4.4-litre V8 petrol engine.