BMW's flagship 8 Series, the M8, isn't due to be revealed for several months, but an undisguised model has already leaked online.

The Mercedes-Benz S-Class Coupe rival is about to go on sale in standard form, with the M8 due to be revealed in mid-2019. Yet a BMW insider has papped images of what looks like a show model of the M-car in flagship Competition form, with no disguise and 'The M8' written on its number plates, and posted them on enthusiast site German Car Forum.

Competition badging features on the car's bootlid, while tell-tale signs this is the full-fat M model include quad exhaust tailpipes and reprofiled bumpers compared with the M850i, the current range flagship.

The M8 is set to make use of the M850i's twin-turbocharged 4.4-litre V8, with upgrades to produce around 600bhp. A 0-60mph time in the low three seconds is expected. It's not clear yet if the M8 Competition will produce even more power, but given the M5 Competition puts out 616bhp to the standard M5's 591bhp, it's more than likely.

Recent patent images, which surfaced on tipster page Ferd, also show the upcoming 8 Series Gran Coupe four-door in its flagship form.

Previewed by the M8 Gran Coupé concept back at the Geneva motor show in March, the Porsche Panamera-rivalling 8 Series Gran Coupé isn't due to arrive until 2019 - several months after the two-door variant. The M8 version arrives a few months after this.

The M-performance M850i will be offered in £76,270 840d diesel and £100,045 M850i petrol form, and the Gran Coupe is predicted to follow suit. The production M8 will be available in all three 8 Series bodystyles, too.

The Gran Coupé is due to enter production in 2019. It appears largely similar to its two-door siblings, but with a raised rear roofline to provide more space for passengers.