Warren Buffett donated 50 Class A shares of Berkshire Hathaway stock worth $27 million to an unnamed charity this week. Those shares remain the most expensive stock out there and were selling for $539,680 apiece Thursday morning. Buffett disclosed the gift in a filing with the Securities and Exchange Commission late Wednesday. This donation is in addition to Buffett's annual gifts to the Bill & Melinda Gates Foundation and four smaller foundations run by his family that he has been making since 2006. Buffett has said that more than 99% of his nearly $118 billion fortune will eventually go to charity. He has been gradually giving away his Berkshire stock over the years.