There are some major differences between the newcomer - to be known as the Sportback - and its three-door stablemate. In fact, externally they don't share a single body panel.
Apart from its two rear doors, the first thing you notice about the car is that it features the all-new Audi family grille. This debuted on the Pikes Peak SUV concept at 2003's Detroit Motor Show, and can now been seen on the A8 W12 and the latest A6. The new nose gives the compact executive car an upmarket feel and from the front immediately distinguishes it from the three-door.
What isn't so obvious from our pictures is that the roofline has been changed slightly to accommodate the rear doors and increase headroom for passengers in the back. Despite this, Audi designers have still managed to keep the A3's rearward sloping coupé-like look, which is accentuated by optional roof rails unique to the Sportback.
There have also been revisions at the rear. The tailgate has been redesigned to enhance the car's practicality, a key area for five-door buyers. The angular panels and tail-lamp clusters - reminiscent of the Nuvolari concept, which was first seen at the Frankfurt Motor Show back in 2003 - complement the upmarket look.
And while the A3 Sportback has the same wheelbase as the three-door variant, Audi's engineers have stretched the back of the car by 68mm to boost rear legroom. This has also enhanced the A3's load-lugging abilities; with the seats up, the Sportback has 370 litres of space - 20 litres more than the three-door - and 1,120 litres with them folded.
A spokesman for Audi told us: "The Sportback is designed to be both stylish and practical. It's aimed at professional people with active lifestyles who want a compact, high-quality car that they can fit their sports equipment in. That's why it looks a bit like a cross between a hatchback, a coupé and an estate."
The A3 Sportback will go on sale in September, with prices starting from around £16,000. From launch, it will be powered by the same range of engines as is available on the three-door A3 - four petrol units and two diesels. However, an all-new turbocharged 2.0T FSI will be added to the line-up within three weeks of the car's introduction.
This unit uses technology from the R8 Le Mans racing car and produces 200bhp and 280Nm of torque, the majority of which is available from 1,800rpm. It's the world's first mass-produced turbocharged direct-injection petrol engine and, according to bosses at the firm, combines excellent performance with impressive economy. It will be offered on other Audi models at a later date. Buyers who want the new 2.0T FSI will be pleased to hear that, as with the 3.2-litre V6 and 2.0 TDI, it's available with the company's acclaimed DSG semi-automatic transmission.
Customers who'd like to give their Sportback a more airy feel will be able to specify a panoramic sunroof from 2005. Called Open Sky, the factory-fit option includes separate blinds to protect against the glare of the sun.