It was inevitable, really. In car manufacturers’ mad dash to lower emissions, petrol-fuelled, V8-engined dinosaurs like the Audi S6 and S7 are heading towards extinction. And just to the underline the point, the brand new S6 and S7 are powered diesel engines backed up by mild-hybrid systems.

Don’t let the S6/7’s eco credentials fool you, though. They are still extremely powerful and stonkingly fast.

The aforementioned diesel engine is a 3.0-litre V6 turbo unit backed up an “electric supercharger,” an electrically-powered, 48-volt compressor that spools up the turbo faster than exhaust gases alone would. The result is sharper throttle response and tree-uprooting power: 350hp and 516lb/ft of torque. There’s more trickery going on with mild-hybrid system, too, which can run the S6/7 on electric power alone at speeds below 13mph.

Mash the throttle and the S6 saloon reaches the 62mph marker in an even five seconds – the S6 Avant and S7 Sportback arrive there 0.1 seconds later. Top speed is limited to 155mph across the board. Those 0-62mph times are over half a second slower than the old V8-powered car. But the trade off is much better fuel economy of around 35mpg, rather 29. Carbon dioxide emissions are considerably lower, too.

An 8-speed automatic gearbox and quattro all-wheel-drive send the power to the road. The power is split 40:60 front to rear under normal circumstances – in extremis, up to 85 percent of the power can be sent to the rear wheels.

Options to sharpen the handling include a torque-vectoring rear differential, all-wheel-steering, adaptive suspension and carbon ceramic brakes. As standard you get the usual selection of driving modes.

As ever, the S6/7 looks little different to a 2.0-litre diesel with an S Line bodykit. The only real giveaway are the quad exhausts. But discretion was the always the point of the S models. The upcoming RS6 and RS7 will shout louder about their potential.

Audi hasn’t announced prices yet, but expect to fork out £60,000 to £70,000. Deliveries start in the summer.