Facebook's Saverin agreed to sell shares to Russian firm in 2010

Thanks to his depiction in the blockbuster film "The Social Network," Eduardo Saverin is one of the social network world's most famous co-founders. But is he now feeling a pinch of seller's remorse after getting rid of some of those uber-valuable founders shares?

Amid a batch of new financial documents released today, Facebook disclosed that Saverin cut a side deal to sell a chunk of his shares to Digital Sky Technologies in 2010. In an attachment to its updated prospectus, Facebook reported that Digital Sky, a Russian-based investment firm, and Saverin were involved in the transfer of shares as part of what it described as the "Saverin Agreement." It's unclear how many shares Saverin sold or what price he received.

In the original S1 filed last week, Facebook revealed that Digital Sky and its affiliates now owns 5.4 percent of the company's outstanding shares. But back on February 19, 2010, Digital Sky and a related party were said to own 8.2 percent of Facebook's outstanding stock.

While pre-IPO estimates of Facebook were already in the tens of billions in 2010, they have since climbed to as much as $100 billion.