For decades, no investment portfolio has been more closely watched by investors than Berkshire Hathaway‘s (BRKA +0.24%)(BRKB +0.25%). Now-retired CEO Warren Buffett always had a knack for spotting amazing deals hiding in plain sight, leading to a greater-than-6,000,000% outperformance of the S&P 500 (^GSPC +0.58%) since the mid-1960s.

But investors might not realize that a “secret” Buffett portfolio exists within Berkshire Hathaway. In the June-ended quarter, this $863 million portfolio sent shares of artificial intelligence (AI) superstars Alphabet (GOOGL +0.35%)(GOOG +0.22%) and Broadcom (AVGO +3.67%) packing. Meanwhile, this under-the-radar fund has built up a significant position in two S&P 500 index funds: the State Street SPDR S&P…