A sponsorship deal with Manchester United ultimately lead to GM's firing of Joel Ewanick.

Details surrounding the firing of General Motors' former marketing head Joel Ewanick are finally coming to light. Ewanick was ousted from his post on July 30 with no explanation from GM.

According to a new report from Bloomberg, Ewanick was fired for failing to reveal the full cost of a sponsorship deal with England's Manchester United Football Club. A series of smaller gaffes leading up to the Manchester deal also hurt Ewanick's stock with GM CEO Dan Akerson.

A whistle blower within GM's marketing department revealed that Ewanick failed to disclose the full cost of Chevrolet's sponsorship of Manchester United. Ewanick reportedly covered up as much as a third of the deal's $559 million price tag by spreading the expense over several marketing budgets.

GM has since revised parts of the sponsorship.

Prior to the Manchester United deal Ewanick was already in hot water with Akerson for two previous public missteps. Just days before Facebook's IPO Ewanick proclaimed that the Detroit automaker was abandoning advertising on the social media site, drawing ire from Akerson. Just days after that, Ewanick went public with GM's decision to suspend all Super Bowl advertising.

So far Ewanick has yet to land a new job.