Leaving the role as the head of Microsoft's Interactive Entertainment business, Don Mattrick has taken on a new position as the CEO of Zynga, the casual/social game publisher, best known as the creators of Farmville.

AllthingsD broke the news earlier this morning ahead of official announcements from both firms. A statement from Zynga explained that former CEO Mark Pincus will be staying on as Chairman of the Board and Chief Product Officer, and that Mattrick's position with Xbox won't be immediately filled (thanks GI International):

"In its short history, Zynga has redefined entertainment and brought social gaming to the mainstream. More than 1 billion people across web and mobile have installed Zynga games, and franchises like FarmVille and Words With Friends have become a part of people's daily lives," said Mattrick. "I joined Zynga because I believe that Mark's pioneering vision and mission to connect the world through games is just getting started. Zynga is a great business that has yet to realize its full potential. I'm proud to partner with Mark to deliver high-quality, fun, social games wherever people want to play.

A memo from Microsoft CEO Steve Ballmer seemed to confirm that Mattrick's role won't be directly filled in the immediate future:

Zynga announced today that Don Mattrick would be its new CEO, effective July 8. This is a great opportunity for Don, and I wish him success. Don’s directs will report to me and will continue to drive the day-to-day business as a team, particularly focused on shipping Xbox One this holiday.

As the public face of major Xbox announcements, including the Xbox One's heavily criticised E3 showing, Mattrick's timely departure at the end of Microsoft's financial year is widely presumed to be influenced by significant restructuring at the company.