Just a few weeks ago, we caught BMW testing a prototype of the new flagship X8 preparing to battle the Audi Q8. While BMW has never sold a full-fat M version of the X7, the X8 will get the full M performance treatment. And, according to Autocar, it will be the Bavarian automaker's most powerful series-production model yet.

Like the X7, the BMW X8 will be offered with a range of six-cylinder gasoline and diesel engines with mild-hybrid technology, while the X8 M50i will pack a 4.4-liter twin-turbo V8 with 523 hp. At the top of the range, the full-fat X8 M will feature a plug-in hybrid powertrain, combining the 4.4-liter V8 with an electric motor and battery.

Insiders claim this setup will produce up to 750 horsepower, making it the most powerful BMW by a significant margin. Internally known as Project Rockstar, the X8 M's electric motor setup will allegedly generate around 200 hp. BMW's xDrive four-wheel-drive system will also be offered, adopting a similar setup to the M8 and M5 with the option to switch to rear-wheel drive on demand.

Adding an electric motor will inevitably add extra weight, but it's not clear if BMW is planning to offer a conventionally powered X8 M with less power and weight. As we've seen in spy shots, the X8 will adopt a distinct design to help it stand out from the X7.

Originally, the X8 was expected to look like a coupe version of the X7, but the front looks flatter than the X7, the roof is lower to give the X8 a sportier look, and the headlights are repositioned. It remains to be seen if the X8 will be offered with seven seats like the X7, but we're expecting the cabin to be even more luxurious.

While the standard X8 is expected to debut later next year and go on sale as a 2022 model, the M version will allegedly arrive a year later. Since the X7 already starts at $73,900, there's a good chance the range-topping X8 M will have a massive six-figure price tag when it goes on sale.