These sketches are the first tangible proof that Lamborghini is on the verge of reprising the four-seater genre after a three-decade hiatus.

Lambo's last four-seater was the front-engined, V12-powered Espada, which was produced from 1968 to 1978.

However, unlike the two-door Espada, the newcomer -- which will be called the Estoque -- embraces a four-door format to rival the upcoming Porsche Panamera (more here) and Aston Martin Rapide.

These sketches, which are the handiwork of Lamborghini's Centro Stile design studio, indicate the four-door will retain many of the styling cues pioneered by the OTT Reventon and Gallardo LP560-4, even though its overall proportions are hardly what we've been accustomed to seeing from the raging bull.

As per the Panamera, Rapide, Merc CLS and Maserati Quattroporte, the Estoque's engine is front-mounted, and its aluminium spaceframe chassis has reportedly been derived from that of the Audi A8.

The engine itself is believed to be a version of the V10 that powers the Gallardo (and Audi S6 and S8), as the V12 used by the range-topping Murcielago is said to be too coarse for the Estoque's 'executive express' job description.

Euro sources suggest the car has been designed to meet all crash-safety and pedestrian-protection standards, which indicates it's destined for production -- rather than merely being a flight-of-fancy exercise.

And in case you're wondering about the Estoque moniker, it's said to be the name of the short sword used by a matador to put the bull out of its misery at the conclusion of a bullfight.

The addition of the third model line (to supplement the Gallardo and Murcielago) would theoretically enable Lamborghini to continue its meteoric sales growth over the past few years.

Bologna's raging bull sold just 424 cars globally in 2002, but by last year that number had swelled to 2580. Profit margins have also been fattened up appreciably during this period, thanks to sourcing parts from its Volkswagen Group parent company.

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