We've managed to catch the BMW 4-Series in the buff.

Following its concept debut earlier this year at the Detroit auto show, our spy photographer have spotted BMW's upcoming 4-Series coupe -- the more shapely companion to the company's volume-oriented 3-Series sedan -- completely undisguised at a night time photo shoot.

For nearly four decades, the car has been known as the 3-Series coupe (the first 3-Series generation was exclusively available with two doors, but a sedan model was added for the second generation). Now, BMW is seeking to differentiate its coupes in response to a general market shift toward more evocative two-doors and more traditional four-doors.

Spy shots

Our most recent spy shots confirm that the 4-Series will feature a more graceful, gradually tapering roofline than the current 3-Series coupe in addition to elongated quarter windows and sporty fender vents. The production 4-Series losses some of the more aggressive design cues from BMW's earlier concept, such as a rear splitter with integrated tail pipes, but still manages to look striking on the streets of the rear world.

Expect the 4-Series to be nearly identical to the 3-Series sedan underneath the sheetmetal. BMW's familiar turbocharged 2.0-liter four-cylinder and turbo 3.0-liter straight-six will likely be on offer, along with a choice of six-speed manual or eight-speed automatic gearboxes. A range-topping M4 model packing a forced-induction straight-six is also part of BMW's plans.