VentureBeat is reporting the creators of one of Zynga’s highest earning games, Words With Friends, Paul and David Bettner are leaving the social gaming giant. The brothers did not publicly explain their reason for leaving or their future plans.

The Bettner brothers joined Zynga back in November 2010 when the company acquired game developer Newtoy (co-founded by the Bettners) for $44.3 million in cash with 1.4 million fully vested shares worth $8.9 million. Words With Friends was already a hit app when Newtoy was acquired, marking a big push for Zynga into the mobile space at the time.

Following the acquisition Newtoy was renamed the Zynga With Friends Studio, which went on to develops games like Gems With Friends, Matching With Friends and Hanging With Friends.

According to our traffic-tracking service AppData, Words With Friends is currently Zynga’s No. 10 most popular Facebook game with 13.5 million monthly active users. On iOS it’s the No. 58 top paid and the No. 73 top grossing app, making it Zynga’s biggest earner on mobile.

The news about the Bettner’s follows a long series of high profile departures from Zynga in the past few weeks including former COO John Schappert, CCO Mike Verdu and CMO Jeff Karp.

Yesterday Zynga also released a preliminary earnings report for its fiscal third quarter which clearly intended to lower expectations. Zynga said it expects to report a net loss between $90 million to $105 million and diluted earnings per share between ($0.12) and ($0.14).