German sports car maker Porsche offered for the first time on Monday a brief glimpse of its most important new product in years, when it published official photographs of its Panamera. Costing over 1 billion euros ($1.26 billion) to develop, Porsche expects to sell at least 20,000 units of the four-door grand tourer annually. Its market debut scheduled for August or September of next year will provide a much-needed boost in volume growth after Porsche suffered two straight years of stagnation at almost 100,000 vehicles. Despite the facelift for its 911 Carrera two-wheel and four-wheel drive cabrios and coupes, the company has furthermore warned it would not be able to escape a severe slump in global car markets, forecasting a drop in volumes for the current fiscal year that ends on July 31. The last time it launched a new model line was December 2002 with the Cayenne SUV, now its best-selling model that accounts for nearly half of all Porsches sold. The Panamera's styling and details follow the design refined over decades on its iconic 911 coupe and later found in the Cayenne as well as the Boxster cabrio and hard-top derivative, the Cayman. The car, which has been speculated to retail starting at 70,000-80,000 euros, is expected to compete with models like the Maserati Quattroporte and Mercedes-Benz CLS, as well as the upcoming Aston Martin Rapide. Volkswagen - soon to be a majority controlled unit of Porsche's European automotive holding company - will supply the painted bodies just like it does with the Cayenne SUV. The vehicle will be assembled at Porsche's Leipzig plant following investments of 150 million euros to expand production at the site, which also houses the Cayenne production line.