Carl Icahn Reveals Large Apple Stake

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Carl Icahn

UPDATED: The billionaire investor tweets that he has advised CEO Tim Cook to buy back more shares "now."

Carl Icahn, the billionaire activist investor who recently made millions with a bet on Netflix, tweeted on Tuesday that he has taken a large stake in Apple, a revelation that caused the stock to spike 5 percent higher.

"We currently have a large position in APPLE. We believe the company to be extremely undervalued. Spoke to [CEO] Tim Cook Today. More to come," Icahn tweeted.

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About four minutes later, Icahn tweeted: "Had a nice conversation with Tim Cook today. Discussed my opinion that a larger buyback should be done now. We plan to speak again shortly."

Icahn, 77, joined Twitter in June and has more than 32,000 followers.

Shortly after Icahn's two tweets were posted Tuesday, Apple stock jumped more than $20 a share. At the end of the trading day, Apple was up 5 percent to $489.57. The stock, though, is down about 30 percent over the past 10 months.

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Icahn's disclosure of an interest in Apple comes three days prior to the opening of Jobs from Open Road Films and Five Star Feature Films, a movie starring Ashton Kutcher as Apple co-founder Steve Jobs.

Icahn's net worth is estimated at $20 billion, which he made by taking stakes in a variety of companies over the past four decades, agitating for change and driving shares higher. Some of the media and entertainment companies he has owned through the years include Viacom, Time Warner, Blockbuster, Lionsgate and MGM.