FRANKFURT (Dow Jones)--Volkswagen AG (VOW.XE) said Monday it has acquired a 49.9% stake in Porsche Automobil Holding SE's (PAH3.XE) core sportscar operations for EUR3.9 billion as planned, and reiterated that the merger with the Stuttgart-based firm is expected to be finalized in 2011.

In a statement, Europe's largest auto maker by sales confirmed it plans to buy the Porsche Holding Salzburg retail operations as the next step.

Last month, Volkswagen's and Porsche's supervisory boards had cleared the way for the tie-up by approving contracts determining details of the complex integration.

The approval drew a line under a fierce power struggle between the two auto makers in recent years.

After some initial in-fighting, Volkswagen has announced that Porsche, not Audi, will take the lead on the group’s future sports car and large luxury sedan offerings. Porsche and Audi have been bickering over which division should take the lead on such projects for the last several months.

The news was reportedly handed down by Volkswagen CEO Martin Winterkorn just before the automaker’s November 30 annual meeting. Porsche joins VW as the group’s 10th automotive brand.

The announcement ensures that Porsche will design the firm’s next-generation “modular standard matrix” platform. That platform is expected to underpin the next Porsche Panamera – which has apparently been green lighted for a second go-around – as well as future Bentley models. Also as part of the deal, Porsche will develop front-mid and rear-mid engine vehicles for Porsche, Audi and Lamborghini.

Audi, meanwhile, will remain in charge of VW’s “modular longitudinal matrix” architecture. First introduced in 2007, the modular longitudinal matrix underpins the Audi A4, A5 and Q5, and will eventually serve as the basis for 15 different vehicles.

The announcement is intended to save VW development time and money, helping the German automaker with its push to unseat Toyota as the world’s largest automaker.

The Volkswagen Group’s three range-topping SUVs – the Audi Q7, Porsche Cayenne and Volkswagen Touareg – are all a few years away from a redesign, but the automaker has named Audi as the engineering lead on the project.

“This decision was made in agreement with all of the brands involved and will create synergies throughout the group to the benefit of both the brand and the customers,” an Audi spokesman told Automotive News.

Porsche is currently in charge of all three models, each of which share platforms but deviate in many other ways.

Audi will also take over development of the upcoming Porsche Cajun, which shares much of its platform with the Audi Q5.

To capitalize on each brand’s expertise, Porsche will be put in charge of developing large luxury sedans and sports cars that will wear Audi, Bentley, Porsche or VW badges. VW, meanwhile, is in charge of smaller platforms – like the new “modular transverse matrix” that will underpin around 40 high-volume models sold as Audis, Seats, Skodas, Seats and Volkswagens.

The move is the latest strategic realignment at VW, which recently merged Porsche to within its global brand portfolio after acquiring just under 50 percent of the sports car brand.

Porsche said late on Wednesday that its merger with Volkswagen would be delayed, and might even be at risk, after German prosecutors told the company they were expanding their inquiry into the carmaker.

Prosecutors said on Thursday that they were investigating former Porsche executives for market manipulation, breach of trust and credit fraud. Those executives include Wendelin Wiedeking and another top executive, Holger P. Härter, according to a person with direct knowledge of the matter.

“The further investigations will be extremely costly and time-intensive, and can in no case be completed before the end of the year,” the prosecutors said in a statement.

Shares of Porsche were down 5.44 euros, or 8.8 percent, to 56.16 euros in Thursday afternoon trading in Frankfurt.

Porsche had planned to get the necessary shareholder approvals for the merger this year. But the deal is predicated on a certain amount of liabilities, and the outcome of the investigation could affect the ultimate numbers. The company now thinks there is a 50 percent chance it will complete the merger this year.

“The overall probability of the merger decreases in case of substantial delays in the merger process,” the company said, adding that it believed a deal could be completed after the end of the year.

Prosecutors were initially looking at whether Porsche manipulated the market through a so-called short squeeze as it attempted to take over Volkswagen in 2008. Porsche, a luxury carmaker, surprised short-sellers of Volkswagen stock by announcing in autumn of that year that it had accumulated more than 74 percent of VW through a combination of stock and call options, driving VW’s share price above 900 euros.

After the stock price skyrocket, hedge funds and investors shorting Volkswagen stock lost billions. VEM Vermoegensverwaltung, a German holding company run by the businessman Adolf Merckle, said it lost hundreds of millions of euros as the result. Mr. Merckle threw himself under a train in January 2009.

Mr. Merckle threw himself under a train in January 2009.