Following rumours about the Alpina B4 growing an extra set of doors for its next generation, our spies have confirmed the new model will be based on the more practical body style. While this may look like a fairly regular BMW-badged four-door 4er, if you know where to look, there are some telltale signs we are dealing with something a bit more special.

The most obvious change is at the back where the partially disguised bumper hosts a more menacing quad exhaust system. Another clue that betrays the car's true identity is the number plate, with "OAL" referring to Alpina's home – Buchloe. Then there's the fact BMW unveiled the new 4 Series Gran Coupe at the beginning of June, so it's a bit too late for a prototype to still carry disguise.

Bear in mind the fact rumours and spy shots strongly suggest a B4 Gran Coupe is en route does not necessarily mean Alpina will skip doing a two-door model. The family-friendly version seen here will serve as a substitute for the M4 Gran Coupe that BMW won't build as the Bavarians think it's not necessary since it would overlap with the M3 Saloon.

According to a report published earlier this year by BimmerPost, production is scheduled to commence in March 2022. Provided the information is accurate, Alpina could decide to unveil the first-ever B4 Gran Coupe before the end of this year or early 2022. The same source claims it's going to be based sold in Europe and slot above the M440i xDrive.

Expect the new model to offer 462 bhp and 516 pound-feet (700 Newton-metres) of torque to mirror the Alpina B3 and its turbocharged straight-six 3.0-litre engine. Performance should also be virtually the same, with the 0 to 62 mph (100 km/h) likely to take 3.8 seconds and the 0-124 mph (0-200 km/h) task around 13.4 seconds. Flat out, the B3 does 188 mph (303 km/h).

In typical Alpina fashion, styling changes will be rather subtle. The tuner's gorgeous 20-inch signature wheels are a given, along with mildly reworked bumpers while the controversial grille design will probably be carried over from the donor car. Upgraded brakes, fully adaptive dampers, and an electronically controlled limited-slip differential are probably on the menu, and so is a re-calibrated eight-speed auto transmission.

Pricing details are not available at the moment of writing, but the Alpina B4 Gran Coupe should bridge the gap between the M440i xDrive models and the two-door M4.