Maserati is just over a year away from revealing the next model in its fast expanding line-up — a new saloon to take on high-end versions of the BMW 5-series and Jaguar XF.

The new sub-Quattroporte four-door, rumoured to be called Levante, is earmarked for a debut at the Frankfurt motor show in September next year. It will be closely related to an all-new Quattroporte that will be seen at the Detroit motor show in January.

The Quattroporte will be pushed further upmarket to give the Levante more space to breathe in the Maserati line-up. The next-generation Quattroporte, codenamed M156, is set to increase in both cost and size, and is likely to be around 5.2 metres long.

Maserati insiders have remained tight-lipped about the architecture of the new saloons, but both are understood to be based on reworked rear-wheel-drive Chrysler 300 underpinnings.

The Levante, codenamed M157, will share a 3052mm wheelbase with the Chrysler 300, while the Quattroporte will in effect be a long-wheelbase version of that car.

The test prototype spied here is the new Levante, hidden beneath the bodywork of the current Quattroporte. The main giveaway that this is a Levante is the location of the front wheels: they are set back in the front wheelarches instead of being sited centrally, indicating a shorter wheelbase.

Both the Levante and the new Quattroporte have been styled ‘in-house’ rather than by Pininfarina, according to Fiat Group insiders. Expect the updated front-end design from last year’s Kubang SUV concept to make it onto the pair of new saloons.

A further indication of the pair’s close relationship is the fact that both will be built alongside each other at the former Bertone factory outside Turin, which Fiat recently purchased. Around €500 million have been spent to bring it up to Maserati production standards.

V8 petrol engines are likely to be offered in both cars, while V6 petrol and diesels will be reserved for the smaller car. An eight-speed ZF auto will be hooked up to all engine options.

The two saloons, along with the production Kubang SUV due in 2014, are part of Fiat chief Sergio Marchionne’s plan to lift annual sales from around 7500 units to 50,000.