Buffett donated about 21.73 million Class "B" shares of Berkshire on Monday, a regulatory filing shows.

About 16.6 million shares, worth more than $2.1 billion, went to the Bill and Melinda Gates Foundation, which focuses on education, health and poverty problems.

The remainder went to four family charities, including a foundation named for his late first wife Susan and foundations for his children Howard, Peter and Susan.

The $2.8 billion is the most Buffett has donated to these charities, reflecting Berkshire's near-record share price, since he began making annual gifts in 2006.

Buffett still controls nearly 20 percent of Berkshire's stock, which made him worth $65.8 billion on Monday, according to Forbes magazine.

Only Mexico telecommunications mogul Carlos Slim and Bill Gates, the Microsoft Corp co-founder and Berkshire director, were worth more, Forbes said.

Berkshire has more than 80 operating businesses and ended March with more than $146 billion of stock and bond investments. Buffett has run the Omaha, Nebraska-based company since 1965.

(Reporting by Jonathan Stempel in New York; Editing by Lisa Shumaker)

By Jonathan Stempel

Stocks treated in this article : Microsoft Corporation, Berkshire Hathaway Inc.