New four-door model looks to provide a sportier alternative to the 7 Series, and should share its powertrain options with the two-door 8 Series range.

The exterior of the BMW 8 Series Gran Coupe has been leaked a few weeks ahead of its expected debut.

These photos were published on the Bimmerpost forum. It's not clear how they were obtained, but they look like legitimate press photos and certainly fit with spy photos we've published in the past.

As with the 6 Series Gran Coupe it effectively replaces, the new four-door 8 Series looks as though it has a longer wheelbase than the two-door models.

Under the skin, the 8 Series Gran Coupe has the same CLAR platform used by almost all of BMW's rear- and all-wheel drive models.

The Gran Coupe's selection of drivetrains will, in all likelihood, be shared with the two-door 8 Series range.

Global launch models should include the M850i xDrive with a 390kW/750Nm 4.4-litre twin-turbo V8, and the 840d xDrive with a 235kW/680Nm 3.0-litre turbo-diesel straight-six.

At some point in the future the 8 Series Gran Coupe range should be topped by an M8 Competition model, which like the coupe and convertible, will be powered by a 460kW/750Nm 4.4-litre twin-turbo V8.

A less powerful 441kW M8 model is also likely, but will probably skip Australian showrooms.