The lesson: Don't count out Berkshire Hathaway. Buffett's retirement announcement. The decision, at the very end of Berkshire's annual meeting, probably surprised a lot of fans who forgot he was 94.

Warren Buffett’s Berkshire Hathaway revealed a position in embattled healthcare giant UnitedHealth Group while showing smaller stakes in longtime holdings Apple and Bank of America, according to a regulatory filing Thursday.

UnitedHealth Group (UNH) stock is still down 40% YTD but has surged more than +20% this month following reports that Warren Buffett, and other billionaire hedge fund managers have taken a stake in the company.

Warren Buffett's Berkshire Hathaway has acquired 5 million shares in UnitedHealth Group , a regulatory filing showed on Thursday, sending the health insurer's stock up 7% in extended trading.

Warren Buffett's Berkshire Hathaway has placed a major bet on a recovery at UnitedHealth Group, disclosing a new $1.6 billion stake in the insurance giant.

Berkshire Hathaway’s portfolio added six new stocks, including the three new secret stocks. Warren Buffett was a net seller of stocks for the eleventh straight quarter.

Berkshire Hathaway just disclosed that it dumped $1.6 billion into a sinking ship, and Wall Street instantly paid attention.