Warren Buffett just announced he has a stake in Apple

Berkshire Hathaway owned 9.81 million Apple shares as at the end of the first quarter.

The stake was worth more than $1 billion at the time, a regulatory filing from the company headed by Warren Buffett showed Monday. It ranked Berkshire as the 56th largest Apple shareholder, Bloomberg reported.

Apple shares climbed more than 2% in pre-market trading after the news crossed.

They fell to a near two-year low last week after another regulatory filing - from Appaloosa Management - showed that David Tepper had dumped his entire stake in the company. Amid the share-price decline, Alphabet (owner of Google) briefly overtook Apple as the world's most valuable company by market cap.

Apple's first-quarter results showed that its revenues fell year-on-year for the first time since 2003. That added to investor concerns about the company, amid a slowdown largely attributed to weakness in China.

Because Buffett's Apple stake was held as at March 31, it's possible that the company has since adjusted the size of its holding.

The filing also showed that Buffett increased his stakes in Phillips 66 and IBM, and sold Walmart shares.