An outstanding engineer, Demant was known as "Mr Opel" after a career spanning nearly 40 years with GM and Opel, including stints as GM Europe's head of engineering for three years from 2001 and Opel managing director from 2004 to 2009.
VW plans to put Demant to work overseeing its new alliance with Suzuki soon after he joins the Wolfsburg automaker on Oct. 1 as head of international project coordination, according to Germany's Handelsblatt paper.
As former head of Opel's small-car unit, Demant worked with Suzuki in developing the Opel Agila small minivan, which is a rebadged Suzuki Splash.
Neither GM or Opel has commented publicly on Demant's defection to archrivals VW. But executives are said to be very angry in private.
GM has only itself to blame. Demant, 59, was sidelined to the post of GM's global intellectual property rights chief in January, two months after he was replaced as Opel boss by GM Europe president Nick Reilly.
Was it smart to shuffle a long-serving top manager into a low-key post? And why didn't Demant have a non-compete contract?