​Carl Icahn unloads his 53 million Apple shares

Billionaire investor Carl Icahn has sold his stake in Apple (AAPL), citing concerns about the giant tech company's prospects in China.

Apple's stock fell 9 percent this week after it reported a sizable drop in iPhone sales. Icahn, a longtime booster, told CNBC he still thinks Apple is a "great company." But he said he worries about Chinese regulators, who recently blocked Apple's online services. The U.S. tech giant has been hoping to expand in China.

Icahn last year called it a "no-brainer" to invest in Apple, predicting the company could be worth $1 trillion. At that point, he owned 53 million shares, valued then at $6.5 billion, nearly 1 percent of the company. The stock has fallen 20 percent since then, but Icahn said he still made $2 billion from selling his shares.