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Berkshire Hathaway CEO Warren BuffettReuters

American billionaire Warren Buffett's investment firm has snapped up a $1bn (£691m) stake in Apple. Berkshire Hathaway disclosed in a regulatory filing that it now holds 9.81m shares in the tech company.

The revelation marks a brave new world for Buffett, who has not traditionally invested in tech companies and has always vowed not to invest in companies he does not understand. He has also said that he does not know how to value tech stocks.

However, Buffett's faith in the company is a boost for Apple, whose shine has grown dull for investors in the wake of slowing iPhone sales. Apple's shares slumped almost 30% since last summer amid Wall Street worries that the iPhone maker is facing a low-growth future.

Apple had temporarily lost its place as the world's most valuable company after a fall in shares depressed its market value below Google's parent company, Alphabet.

But shares in Apple jumped 3.7% to $93.88 in trading after Berkshire Hathaway's stock purchase revelation, boosting the company's market value by more than $18bn (£12.5bn).

Buffett did not personally make the investment himself, the Wall Street Journal reported. The purchase order was likely placed by his stock-picking team Todd Combs and Ted Weschler, who tend to take risks where Buffett may not.

Buffett recently admitted at Berkshire's annual meeting earlier this year that his investment firm had been slow to dip into the tech industry.

The firm seems to begin to be making up for lost time in tech investments. Berkshire Hathaway is now the biggest shareholder in IBM and recently increased its stake. But for now it is only the 56th largest stockholder in Apple.

Buffett also recently revealed that he is willing to help Dan Gilbert, the billionaire founder of Quicken Loans, finance a bid for Yahoo's internet business.

Buffett has long been a fan of inexpensive stocks with predictable cash flows. He has been skittish about tech stocks that can be quickly undermined by mercurial tech markets, the Financial Times noted.

Buffett's interest "signals a change in the kind of company Apple is," Gene Munster of Piper Jaffray, one of the most bullish analysts on Apple, told the Financial Times. "There are new investors. It used to be growth and high-risk investors, now it's more value and return on capital."