For the past 14 years, the 6 Series has been a flagship two-door coupé. But from September, when it's officially relaunched in Frankfurt, it's set to become a four-door luxury GT instead.

According to the company's global head of sales and brand, Dr. Ian Robertson, the BMW 6 Series Gran Turismo will offer: "Unique combination of luxurious interior comfort and flexible practicality, packaged within a truly elegant design."

So, the car has a coupé shape, but it has four doors and, because of a deeper rear trunk line, actually offers more luggage space than a BMW 5-Series Touring (the company's nomenclature for an estate or station wagon).

However, if the car sounds familiar, it's because until now, it's been called the 5-Series Gran Turismo.

Yet its replacement is more than simply a name change. It is 150kg lighter thanks to greater use of aluminum and its exterior lines are tighter so that the rear end doesn't look as bulbous as on the original model. The new car is 87mm longer, yet the roofline has been dropped by 21mm and the width remains unchanged. These and other aesthetic changes have also boosted the car's aerodynamic properties so that it is faster off the line yet more efficient.

For example, the 630i model will hit 100km/h 0.7 seconds faster than the outgoing 5 Series equivalent yet across the initial range (there will be three engine variants available at launch) BMW is managing fuel consumption and emission figures that are as much as 15 per cent better.

As one would expect from a company with a short-term goal of launching a real-world autonomous car within the next five years, the 6 Series is bursting with latest-generation active driver aids. It can help out on the highway, maintaining lane discipline -- a safe distance from the car in front -- and can take over the monotony of stopping, starting, rolling forward and stopping again when the road is congested. It can also auto steer even at speeds in excess of 100mph (in highway driving conditions), park itself at the touch of a smart key button and, in busy urban environments, run web searches for available on-street parking berths.

In terms of long-distance cruising capabilities, the car comes with self-levelling air suspension for when the trunk is fully loaded. The tailgate opens and closes automatically, and the rear seats can be folded down electronically.

In 2018, BMW will launch the 8 Series. This will be a new uber-luxury uber-sporty GT coupé and it will sit at the very pinnacle of the company's model range. And to ensure that it really stands out, the company has decided to retire the 6 Series in its current form to make way and to create model clarity.

The BMW 6 Series GT will make its official debut at the 2017 Frankfurt International Motor Show on Sept. 14.