In Google’s IPO prospectus 21 years ago, founders Larry Page and Sergey Brin gave a flattering nod to Warren Buffett, suggesting in their letter to prospective investors that the billionaire investor was a big influence.

They titled their founders’ letter, “‘An owner’s manual’ for Google’s shareholders,” and indicated that there was a footnote worth reading.

“Much of this was inspired by Warren Buffett’s essays in his annual reports and his ‘An Owner’s Manual’ to Berkshire Hathaway shareholders,” the footnote said.

More than two decades later, Buffett is showing that the admiration goes both ways. Berkshire Hathaway, Buffett’s holding company, revealed late Friday that it owns a stake in Google parent Alphabet worth roughly $4.3 billion as of the end of the third quarter, making it the firm’s 10th largest equity holding. It marks one of Berkshire’s most significant technology bets in years — Apple’s is the firm’s largest holding — and sent sent Alphabet shares up 3% on Monday.

It’s a rare move by Berkshire, which for decades has hesitated to buy into high-growth tech companies, and represents the first time the firm is known to have a stake in Google. Buffett, 95, is stepping down as CEO at the end of this year, with longtime lieutenant Greg Abel set to take the reins.

In 2017, Buffett said he regretted not buying shares in Google years earlier when Berkshire insurance subsidiary Geico was paying hefty fees for advertising on its network. He also acknowledged missing out on Amazon, which Berkshire eventually purchased in 2019, still owning $2.2 billion worth of the e-commerce shares.

Alphabet shares are up 50% this year, after Monday’s gains, trading just shy of their all-time high reached last week. The company notched its first $100 billion revenue quarter in the third period, fueled by growth in its cloud unit, which houses its artificial intelligence services. The cloud division also has a $155 billion backlog from customers and an updated line of chips that sets it apart from other AI players.

Alphabet’s valuation remains lower than many of its AI-driven megacap peers. The stock trades at about 26 times next year’s earnings, compared with Microsoft at 32, Broadcom at 51 and Nvidia at 42, according to FactSet.

Page and Brin are now ranked seventh and eighth, respectively, on the Forbes billionaires list, just behind Buffett at sixth.

The Google founders cited Buffett multiple times in the company’s IPO prospectus. In one instance, Page and Brin were effectively warning investors that quarterly financials may not always look pretty.

“In our opinion, outside pressures too often tempt companies to sacrifice long term opportunities to meet quarterly market expectations,” they wrote. “In Warren Buffett’s words, ‘We won’t “smooth” quarterly or annual results: If earnings figures are lumpy when they reach headquarters, they will be lumpy when they reach you.'”

In explaining the logic behind a dual-class stock structure, which gave the founders outsized voting control, they cited Berkshire as one of the companies to previously and successfully implement it, along with media companies like The New York Times, the Washington Post (the newspaper now owned by Jeff Bezos) and Wall Street Journal publisher Dow Jones (now owned by News Corp.)

“Media observers have pointed out that dual class ownership has allowed these companies to concentrate on their core, long term interest in serious news coverage, despite fluctuations in quarterly results,” Page and Brin wrote. “Berkshire Hathaway has implemented a dual class structure for similar reasons.”

WATCH: Berkshire discloses new Alphabet state worth $4.3 billion.