The Federal Reserve's decision to restrict the growth of Wells Fargo  (WFC) until it improves its corporate governance practices sent shares of the bank sharply lower in after-hours trading, costing its biggest shareholder, Berkshire Hathaway (BRK.A) , close to $2 billion.

Wells Fargo is famously Warren Buffett's largest single investment, and even after trimming some shares last year, the Oracle of Omaha still held more than 450 million shares of the bank, according to the latest 13F filing with the SEC from November.

Before Friday's close, and even with the market downdraft, those shares were worth almost $30 billion. But after news of the Federal Reserve's unprecedented action against the bank, the stock fell $3.98 a share in late trading to $60.09. That move took more than $1.8 billion off the value of Berkshire's holdings.

Of course, nothing ever turns out too badly for Buffett, and since shares of Wells Fargo had gained nearly 10% just since November, he's still ahead on the deal.

Now what with these markets? TheStreet's Executive Editor Brian Sozzi and reporter Kinsey Grant discuss.

Inside Friday's Jaw-Dropping Market Selloff

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