Investment guru Warren Buffett confirmed Wednesday the trimming of his Apple, Inc. (NASDAQ:AAPL) stake and finally shed light on the mystery stock his firm, Berkshire Hathaway, Inc. (NYSE:BRK) (NYSE:BRK), accumulated ahead of the first quarter.

Apple, Chevron Trimmed: Berkshire reduced its Apple position by a little over 116 million.

The firm now owns 789,368,450 Apple shares valued at $135.36 billion, a 13F filing shows. This is the second straight quarter that the Buffett-led company has diluted its Apple stake.

The iPhone manufacturer remains Berkshire's top holding.

Earlier this month, Buffett — at the annual Berkshire shareholder meeting — said the dilution has to do with footing the tax bill and the desire to hold more cash due to economic uncertainties.

After adding 15.9 million Chevron Corp. (NYSE:CVX) shares in the fourth quarter, the firm sold 3.1 million shares of the oil giant in the first quarter. The latest 13F showed Berkshire owning 112.98 million shares worth $305.70 million.

But Berkshire added 4.32 million shares of Occidental Petroleum Corp. (NYSE:OXY), with its latest stake amounting to 248.02 million.

Berkshire maintained its stake in its other three core holdings:

• Bank of America, Inc. (NYSE:BAC): 1.03 million shares valued at $39.17 billion
• American Express Co. (NYSE:AXP): 151.61 million shares valued at $34.52 billion
• Coca-Cola Co. (NYSE:KO): 400 million shares valued at $24.47 billion

Mystery Stock Unveiled: Berkshire also finally disclosed the mystery stock it sounded out earlier. The firm bought a big chunk of Chubb Limited (NYSE:CB) shares.

Berkshire accumulated 25.92 million shares of the property and casualty insurer at a valuation of $6.72 billion. This stake gives Berkshire a 6.4% stake in the insurer (based on 406 million in outstanding shares).

Insurance has been a staple sector in Berkshire's portfolio. Other holdings include auto insurer GEICO, reinsurance company General Re and Alleghany Corporation, a holding company of property and casualty reinsurance and insurance operating subsidiaries.

HP Stake Jettisoned: Berkshire cashed out of HP Inc. (NYSE:HPQ) in the first quarter. The firm sold all the 22.85 million shares (worth $687.64 million) of the computer and peripherals maker it held at the fourth quarter.

Other Disposals: Among the other portfolio stocks, the firm part disposed include:

At the shareholder meeting, Buffett previewed the Paramount Global sale and took the responsibility for zeroing in on the investment.

"It was 100% my decision, and we've sold it all, and we lost quite a bit of money," he said.

Berkshire Hathaway's Class A shares were little changed at $413.01 in premarket trading, according to Benzinga Pro data.

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