Warren Buffett is now the world's second-richest person as Berkshire Hathaway's stock rallied to an all-time high.

Forbes said its real-time ranking of the world's billionaires now estimates Buffett's wealth at $74.4 billion, about $1.5 billion more than Carlos Slim's $72.9 billion. Slim is now in third place.

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Class A shares of Buffett's Berkshire Hathaway closed at a record $227,800 after hitting an all-time intraday high of $229,374 in Monday's trading. They're up 28 percent for the year, trouncing the S&P's 11.5 percent gain, excluding dividends.

In March, Forbes estimated Buffett's fortune at $58.2 billion. He was No. 4 on the list at that time, behind Mexico's Slim with $72 billion and Spanish fashion executive Amancio Ortega with $64 billion.

Forbes notes that Slim's net worth has dropped $2 billion since its peak in early September. At that time he was the world's richest person. Since then, shares of his America Movil company have been pressured by expectations it will have to sell assets to keep its market share below 50 percent, as required by new antitrust regulations in Mexico.

Microsoft's Bill Gates currently at the top of the Forbes list with an estimated $81.4 billion.