Chang said he integrated his network with theirs and then they later formed the Winklevoss Chang Group. As partners in WCG, he said, they launched products, met with big-name companies about projects, developed new technology and shared a joint bank account. The suit includes e-mails and instant messages purportedly between the two parties showing that the WCG presented itself to outside companies as a unified company, of which Chang said he owned 50 percent.
But in April 2005, he said, after disputes over shares in WCG and the Winklevosses' refusal to fund the company's operations, the brothers told Chang they wanted to end the partnership. At the time, Chang said, the company had little revenue and few liquid assets.
In September, after being sued by the Winklevosses over ConnectU, Facebook counter-sued ConnectU over a product called Social Butterfly. In that suit, Chang is listed as defendant.
Chang said the Winklevosses hired lawyers to represent them all and paid for his legal counsel in the Facebook suit. But he said that as proceedings continued, the group's lawyers sidelined him and didn't advise him regarding his ownership rights and interests in ConnectU and WCG.
It was from a 2009 news story -- and not his own lawyer -- that Chang said he learned that Facebook had settled with ConnectU for a reported $65 million.
"I didn't even know that a settlement like that was possible," he said. "My attorneys kept me in the dark."
In the complaint filed last year, Chang also sues the lawyer representing them, Scott Mosko and his firm, for professional negligence, claiming they ignored his interest in favor of the interests of their other clients.
As part of the settlement, the Winklevosses turned over 100 percent of ConnectU's stock to Facebook. Believing that his 15 percent ownership in ConnectU and 50 percent ownership in the Winklevoss Chang Group entitled him to a portion of the settlement, Chang said he started pursuing legal options in early 2009.
George Grellas, a Silicon Valley attorney with decades of experience with early-stage start-up companies, said it's not unusual for start-ups to form partnerships without extensive documentation and legal counsel.
"What most people don't realize is that you just need to have a situation where people are acting as co-owners for profit and it doesn't have to be a formal written agreement. It doesn't have to be anything that lawyers sign off on," he said. "What the law looks at is their intent."
From reviewing the complaint, he said, it seems that this particular case includes an unusually large set of documentation (including the e-mails, instant messages and informational material about the project).
But, he said, it's possible that the defendants could argue that the documentation establishes that the parties were only negotiating a partnership, not that they had actually moved forward with it.
Although Chang's complaint is about a year old, attention on his suit has been renewed, thanks to publicity surrounding "The Social Network" and the Winklevoss' efforts to appeal their settlement, saying they are owed more because Facebook misled them about the value of the company.
In the "60 Minutes" earlier this month, the twins said the appeal was not about money, but "principle."
But Chang said that to him, those words ring hollow.
"I've heard the Winklevosses speak of doing the right thing and being ethical," Chang said. "That's definitely not my experience with them. They made promises to me in writing and they refuse to live up to their promises."