Facebook Inc. co-founder Eduardo Saverin’s stake in the world’s most popular social-networking company is worth $2.1 billion, a regulatory filing shows.

Saverin, 30, owns 53.1 million shares of the company’s Class B common stock, according to a May 17 filing with the U.S. Securities and Exchange Commission. Saverin started Facebook with Mark Zuckerberg and two other Harvard University classmates in 2004.

The Brazil-born billionaire renounced his U.S. citizenship last year and is now a permanent resident of Singapore.

“I am obligated to and will pay hundreds of millions of dollars in taxes to the United States government,” he said in a May 17 statement.

Facebook raised $16 billion in an initial public offering, selling 421.2 million shares for $38 each on May 17. It was the biggest technology IPO in history.

The company’s shares advanced 5.3 percent to $40.01 at 2:46 p.m. in New York after earlier trading at the IPO price of $38, which valued the company at $104.2 billion.