Warren Buffett has said that he underestimated Amazon.com Inc.’s Jeff Bezos. Now one of Buffett’s deputies is willing to put money behind the tech giant.

Berkshire Hathaway Inc. has been buying Amazon shares and the purchases will show up in a regulatory filing later this month, Buffett told CNBC in an interview Thursday. Buffett, Berkshire’s chairman and chief executive officer, said “one of the fellows in the office that manage money” made the purchases, a reference to investment managers Todd Combs and Ted Weschler.

Combs and Weschler have gained influence at Berkshire in recent years. Buffett credited some of his conglomerate’s purchases of airline stocks and Apple Inc. to the deputies and noted their involvement in helping Berkshire beyond their stock-picking duties. Buffett, 88, and long-time business partner, Charles Munger, 95, have praised the pair, with Munger saying they give Berkshire “younger eyes.”

The Amazon stake further cements the relationship between Berkshire and Bezos’s company. Berkshire is a partner with Amazon and Wall Street bank JPMorgan Chase & Co. in a health venture. The firms are setting up an independent company to offer health-care services to their U.S. employees more transparently and at a lower cost.

Amazon’s stock, up 27 per cent this year at Thursday’s close, climbed 2.1 per cent in pre-market trading in New York Friday. Buffett’s assistant didn’t immediately respond to a message seeking comment.

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Buffett said in the CNBC interview that he has been “a fan” of the online retail giant and “an idiot for not buying” shares in the past. He was speaking ahead of Berkshire’s annual shareholders meeting, set for Saturday in Omaha, Nebraska.

Buffett has mostly avoided technology-related stocks over the years, saying he didn’t understand the products and markets well enough. One exception was International Business Machines Corp. His $10 billion investment in the computer giant in 2011 was a curiosity for Berkshire, and it didn’t end well. After taking losses, Buffett had sold nearly all the IBM stock by 2018.

Then in 2016, Berkshire jumped into Apple and has built his stake in the iPhone maker into a holding valued at more than US$50 billion. Buffett bought Apple and Amazon when they weren’t at their cheapest. Amazon closed Thursday at US$1,900.82 and Apple traded at US$209.15. Still, Berkshire ended 2018 with its Apple investment valued more than the cost of buying the shares.

Previously: Buffett Drew Lessons From IBM as He Entered, Then Exited, Oracle