Billionaire investor Carl Icahn revealed on Twitter that he's taken a "large position" in Apple.
"We believe the company to be extremely undervalued," Icahn said Tuesday. Icahn's investment in Apple is worth over $1 billion, the Dow Jones reported.
Apple stock spiked as much as 5.69 percent on the announcement and closed up 4.75 percent, making it the iPhone maker's second best day of the year. (Click here for the latest Apple quote)
While Apple is now up over $100 from its 52-week low of $385.10 hit on April 19, it remains down about 8 percent for the year.
Icahn said he spoke with Apple CEO Tim Cook about the company launching a larger buyback and that the two plan to speak again. A buyback is a "no brainer" for Apple, Icahn told CNBC on Tuesday. It would enhance the stock value tremendously, he said.