Shares of Blackberry slipped on Thursday, after the company's former Co-Chief Executive Officer Jim Balsillie disclosed that he had sold his once-sizable stake in the embattled smartphone maker.

In a regulatory filing on Thursday, Balsillie said that by the end of last year he had sold his entire stake in the company. Balsillie, who stepped down as CEO a year ago, owned about 26.8 million shares, or a roughly 5 percent stake in the company, as of December 31, 2011.

Shares of BlackBerry were down 3.4 percent at $13.52 in early trading on the Nasdaq, while its Toronto-listed shares fell 3.5 percent to C$13.51.

(Reporting by Euan Rocha; Editing by Gerald E. McCormick)