In the process of preparing for its upcoming IPO, social game developer Zynga (News - Alert) has been forced to open up its vault and unearth a number of secrets, some more well-kept than others.

The Farmville maker filed a 619-page document with the SEC on Monday that details its comprehensive investor list as well as its complicated yet very close relationship with Facebook (News - Alert), the startup's chief gaming platform.

The document confirmed widespread speculation by placing Google on the very top of the investor list. The search engine giant's positioning on the list doesn't necessarily indicate that Google (News - Alert) contributed more of the $845 million in funding than others, but it does mark the first time that Zynga has acknowledged the poorly-kept secret. TechCrunch ran a story more than a year ago that said Google has invested at least $100 million in the thriving game maker.

All Things Digital's Tricia Duryee has speculated that the investment could be even larger, and may be related to the rumor that Google+ is planning its own social gaming network.

Other well-known Zynga investors named in the document include Japan’s Softbank, VC firm Kleiner Perkins Caufield & Byers and Peter Thiel, an early Facebook investor.

The other big news revealed in the SEC (News - Alert) filing involves its closest partner, Facebook. After going through the document with a fine tooth comb, AllThingsD's Liz Gannes found some very interesting details on the companies' relationship.

First off, Zynga has agreed to give Facebook exclusivity for any game that is integrated into the social network or uses its data – at least for the duration of the agreements, which are not known. In addition, Zynga is required to tell Facebook about any game that launches on its platform at least a week before it will debut. The soon-to-be public company is also prohibited from launching games on rival social networks, whose names are redacted in the document.

However, according to a Facebook spokesperson, "We don't have agreements with any developers, including Zynga, to share revenue from ads next to their Facebook canvas apps. We did agree with Zynga to work together in the future on providing ads on their properties beyond Facebook, but we have no current timeline for when we might start working on that." 

It will be interesting to see if the relationship entices investors or makes them fearful of the lack of control that Zynga has over its own operations. After all, the filing paints Zynga as more of a Facebook subsidiary than an autonomous company.

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