Diess (Photo: BMW)

BMW's Herbert Diess will take over as head of the Volkswagen brand three months earlier than originally planned, following an agreement between Europe's largest auto group and the Munich-based premium car maker.

VW said Diess, formerly head of R&D at BMW, will take the helm at the VW brand July 1, rather than October 1, as was originally planned.

Diess will succeed VW Group CEO Martin Winterkorn, who in recent years has also headed the company's core passenger-car brand. Winterkorn will continue as group CEO, but Diess is widely considered a potential successor  to run the entire company. A few other VW board members are also seen as contenders. It is unclear when in coming years Winterkorn plans to retire.

At VW brand, Diess will be tasked with shoring up the profitability of the volume car division, which has been lagging  behind the rest of the group. And he will need to focus attention on the US market, where VW hasn't been able to meet its ambitious growth targets.