(Reuters) -- Volkswagen AG supervisory board Chairman Ferdinand Piech unexpectedly resigned Saturday after losing a showdown he provoked with CEO Martin Winterkorn. Piech, a dominant figure at VW for more than two decades and the grandson of the inventor of the VW Beetle, also resigned as member of the supervisory board and any other mandates within the Volkswagen group with immediate effect, the company said.

The leadership row at VW burst into the open this month when Der Spiegel quoted Piech, the 78-year-old patriarch of the family that owns 51 percent of voting rights in VW, as saying he had “distanced" himself from Winterkorn. The comment came at a time when VW is cutting billions of euros of costs and revamping structures to boost profitability, having struggled with underperformance in the U.S. and declining profitability at its core autos division.

Tensions between Piech and Winterkorn appeared to have eased a week ago when senior supervisory board members backed the CEO, leaving Piech isolated in a five-to-one vote and forcing him to agree to a joint statement supporting Winterkorn. But sources said at the time he would have faced calls for his own resignation had he not backed the CEO.

Deputy Chairman Berthold Huber will temporarily assume leadership of the board until the election of a new chairman, Volkswagen said, adding that Piech’s wife Ursula had also resigned from her mandates at the group.

(Reporting by Maria Sheahan; Editing by Thomas Atkins and Georgina Prodhan)