As chief executive at Bertelsmann from November 1998 through July 2002 , Mr. Middelhoff nudged the staid company and its owner , Reinhard Mohn , a distant relative of Bertelsmann 's founder , to sell a 25 percent stake to a Belgian investor , Baron Albert Frere , and his Canadian partner , Paul Desmarais , who have the option of listing their shares and taking the private media company public .