Regulatory filings revealed Monday after the stock market closed that Peter Thiel, Facebook's first big investor, shed most of his holdings in the social networking icon.
Thiel is also a board member.
Thiel originally invested $500,000 in Facebook in 2004. He sold 16.8 million shares in the company's May 18 IPO and another 20 million or so late last week after a lockup period banning the sales expired. In all, he's reaped more than $1 billion from the sales.
On Monday, Facebook's shares hit a new low of $18.75 before bouncing back to $20.01 by the time the market closed. But Tuesday saw the stock dip 85 cents, 4.3 per cent, to close at $19.16.