The ex-chairman of Volkswagen, Ferdinand Piech, who is seen as responsible for its rise from the brink of bankruptcy, is said to be in talks to sell his stake in the group.

The 79-year-old owns 14.7% of Porsche SE, which in turn controls the Volkswagen group, with 52% of its voting rights.

The stake owned by the former chairman is worth more than a billion euros, according to the Web site Spiegel Online, which first revealed the talks and said they follow differences with Porsche’s founding families.

The negotiations cover the sale of “the major part” of Piech’s Porsche SE holding to the Porsche and Piech families, which have first rights on the purchase, Porsche SE said in a statement.

Relations with the current management and the other co-owners of VW apparently became strained after Mr Piech claimed that company chiefs — including CEO Martin Winterkorn — knew about the emissions cheating (that led to the so-called diesel-gate scandal) earlier than they admitted. In February, board members targeted in Mr Piech’s allegations rejected them as “false”.

An internal investigation had examined his claims last year and found no evidence, they said. According to the German newspaper Bild, Mr Piech told prosecutors in the German city of Brunswick that he heard rumours about the emissions fraud in February 2015, while he was still chairman of the supervisory board.