He's using most of the windfall to cover taxes.

Facebook CEO Mark Zuckerberg will sell about $2.3 billion worth of shares in the company, slightly reducing his stake and voting power at the social network company, Facebook said Thursday.

Zuckerberg will sell 41.4 million shares as part of the firm’s stock offering of 70 million Class A common shares, reducing his voting power to 62.8 percent from 65.2 percent, according to a public filing by the company. The filing says Zuckerberg will use most of the windfall to pay taxes connected to his exercising an option to buy 60 million Class B common stock, the majority of which is being converted to Class A stock and sold in this offering, the filing said.

Venture capitalist and board member Marc Andreessen will also sell some 1.6 million shares worth about $89 million, and Facebook will sell another 27 million shares.

Facebook’s stock has doubled this year and closed Wednesday at $55.57.