NEW YORK, United States — Lululemon Athletica Inc. founder Chip Wilson will sell half his stake in the yogawear company to private equity firm Advent International for about $845 million.Wilson and Advent agreed to name David Mussafer and Steve Collins to the board of directors, effective as of the closing of the transaction, expanding the board to 12 members from 10, Lululemon said in a statement. Mussafer will become co-chairman with Michael Casey.Wilson, who agreed to resign as Lululemon’s chairman in December, has been voicing his displeasure with the company’s current direction. On June 11, he said he voted unsuccessfully against the re-election of Casey, his successor.Advent and Wilson also signed a standstill agreement, agreeing not to pursue any kind of buyout action through the 2016 shareholder meeting. Advent had previously invested in Lululemon in 2005 and worked closely with Wilson and five of the current directors, including Casey, to help the company expand from a regionally focused retailer to a global brand. Advent exited its original investment in June 2009.By Lindsey Rupp; editors: Nick Turner, Cecile Daurat, James Callan.