The car known simply as the Audi 'Urban Concept' is turning out to be one of the more vocal concepts of the upcoming 2011 Frankfurt Auto Show.

It was originally spied on the streets of Berlin. After the cat jumped out of the bag, Audi came clean with the official press release and renderings. And now a twist that we didn't see coming (and didn't necessarily want to see): The Urban Concept comes in Spyder open-top bodystyle.

We knew from Audi's initial press release that the urban concept's roof and doors slide backwards to allow for entry, but as it turns out, the roof can come off altogether. Albeit in a separate model.

As you can quickly see when comparing pictures, the wraparound greenhouse on the convertible is entirely different from the larger windshield and retracting side-door windows on the original. The convertible is an airier alternative to the tiny hard-top.

All the other exterior hardware looks the same, including the skinny, freestanding, 21-inch wheels and flat nose. The only difference is that the tires are traditional black rather than white.

The Spyder also retains the same 1+1 layout, ultralight build, lithium-ion battery and dual-motor powertrain as the hard-top.

Both variants of the Urban Concept will appear at the 2011 Frankfurt Auto Show, which opens to media on September 13. Follow our complete coverage of the event thus far, by clicking here.