A prototype of the all-new Infiniti G sedan has been spotted in the final stages of testing in Europe ahead of its international premiere at the 2013 Detroit motor show in January.

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With its sights firmly set on the likes of the BMW 3 Series and Mercedes-Benz C-Class, the mid-sized G sedan will become the centrepiece of the Japanese sports luxury manufacturer’s global line-up when it hits showrooms during the second quarter of next year and launches in Australia at the end of 2013.

The spy images confirm the all-new Infiniti G sedan will take a generational leap forward from a design perspective, with the 2013 model drawing inspiration from a number of the brand’s recent concept vehicles.

Infiniti’s signature grille will be upright and prominent on the new G sedan, appearing somewhat reminiscent of the Jaguar XF and XJ, while the headlights make the transition from swept back and tall on the current model to low and wide, creating a more sinister appearance.

Bold contours in the bonnet and door panels bring a new sense of fluidity and personality to the medium sedan, while the heavily raked rear window takes the coupe-style profile of the outgoing car to a new level.

Like most overhauled models, the new Infiniti G sedan looks slightly larger than the car it will replace, which should create a more spacious cabin.

As CarAdvice reported in September, the new 2013 G sedan will sit on a rear-wheel drive Nissan Motor Co platform and will be offered with three Mercedes-sourced engines – a 3.0-litre V6 diesel, a four-cylinder diesel and a turbocharged 2.0-litre petrol – as well as an upgraded version of the current car’s 3.7-litre V6 petrol.

The new four-door sedan will be the first model from the new-generation Infiniti G line-up, which is expected to expand to include a coupe, convertible and potentially a wagon for Europe.

Infiniti will introduce the current G family to Australia at next week’s 2012 Sydney motor show before launching the coupe and convertible across the country in December.