Apple shares have hit an all-time high on news that legendary investor Warren Buffett now has a roughly 5% stake in the tech giant.
Shares in Apple, already the world's most valuable company, rose by almost 4% on Friday to more than $183.7 each.
Mr Buffett said his Berkshire Hathaway group bought about 75 million more shares of the iPhone maker in the first three months of the year.
His investment moves are closely watched across the world.
Mr Buffett's company has been buying up shares in Apple since 2016. Berkshire Hathaway claimed a nearly 3.3% stake, or more than 166 million shares, at the end of last year.
At the time, the holding, one of Berkshire's biggest stock market gambits, was worth more than $28bn.
Now, after the additional share purchases and an 8% rise in price since the start of the year, the firm's stake is worth more than $44bn.
Apple's market value now stands at almost $932bn.
"It is an unbelievable company," Mr Buffett said in an interview with CNBC. "If you look at Apple, I think it earns almost twice as much as the second most profitable company in the United States."
Some analysts have worried the technology giant's best days are behind it, as competition in the smart phone market increases and sales growth slows.
But the company has been building up other lines of business, including the services unit that includes the App Store, Apple Music and Apple Pay.
Apple this week reported profit of $13.8bn in the first three months of the year, rising 25% from the same period in 2017.
The company also has a generous share buyback and dividend programme that is expanding.
Apple, citing new US tax cuts, this week said it would buy back $100bn worth of shares and increase its dividend.
The moves, which return money to its shareholders, had been widely anticipated in the aftermath of the new tax law, which lowered the corporate tax rate and reduced the incentives for firms to hoard cash overseas.
Berkshire Hathaway will host its annual meeting for shareholders in Omaha, Nebraska this weekend.