A new Buick coupe has been reported on for more than a year but the first tangible evidence that the car might be coming has only recently surfaced. A leaked document reportedly outlining GM Europe’s future plans claims that a new coupe based on the Insignia sedan and its Epsilon II platform is in the works, and this very well could come to the U.S. as a new Buick flagship.

For the uninitiated, GM’s Opel Insignia sedan is already sold in the U.S. as a Buick Regal, so a coupe version could be sold here as well. Furthermore, GM has already previewed a coupe version of the Insignia with the unveiling of 2007’s Opel Gran Turismo Coupe (GTC) concept car (pictured above).

That concept was originally built to preview the design of the soon-to-be released Insignia sedan but its stylish coupe body is just begging to be turned into a production model.

If built, the Buick version could serve as a halo model for the brand, picking up the Opel Insignia OPC model’s trick all-wheel drive system and 325 horsepower turbocharged 2.8-liter V-6. Acceleration figures would be nothing short of amazing, with 0-60 times of around 5.0 seconds possible.

Sadly, the Insignia coupe isn't expected in Europe until 2013, meaning it would wait at least that long before coming to America. One thing that could bode well for its arrival on our shores is that Opel would need to sell 30,000 units each year to make a business case for the car. That would be tough to achieve in Europe alone, but exporting them to the U.S. could bolster their numbers significantly.

Interestingly, the sporty coupe isn’t the only new model expected to join the ever-expanding Buick lineup. The recently revealed Astra GTC three-door hatchback is reportedly set to join the Buick lineup, as is a new Astra-based convertible model.

Stay tuned for an update.