Berkshire sold 20.7 million of those shares in the third quarter of 2024, but its 86.4 million remaining shares are still worth $949 million and give it a 1.8% stake in the company. Berkshire's stake in Nu only accounts for 0.3% of its entire portfolio, but the Latin American bank is still growing much faster than its brick-and-mortar competitors.

Warren Buffett and his team at Berkshire Hathaway (NYSE: BRK.A)(NYSE: BRK.B) have long dabbled in bank stocks, owning almost every major Wall Street bank at one time or another over the past several decades.

The third industry-leading AI stock Warren Buffett secretly owns shares of via New England Asset Management is Alphabet (NASDAQ: GOOGL)(NASDAQ: GOOG). Despite NEAM selling shares of Alphabet for five consecutive quarters, the fund still held 5,195 Class A shares (GOOGL) as of Sept. 30.

Warren Buffett Owns 6 Dow Jones Stocks. Here's the Best of the Bunch for Income Investors to Buy Right Now.