Ichan, Chairman of Icahn Enterprises, revealed the Apple investment on Twitter:
"We currently have a large position in APPLE. We believe the company to be extremely undervalued. Spoke to Tim Cook today. More to come."
And sure enough, minutes he later 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, describes himself as "Chairman of Icahn Enterprises L.P.; etc., etc. Some people get rich studying artificial intelligence. Me, I make money studying natural stupidity", recently sought to stop Michael Dell from taking the PC company he founded, private.
He also previously sought to shake up Yahoo! and Motorola.
In April, Apple kicked off a massive US$60 billion stock buyback, but Icahn now believes this can be enlarged to a $150 billion buyback by borrowing funds at 3 per cent, he told Reuters.
"If Apple does this now and earnings increase at only 10 percent, the stock - even keeping the same multiple currently - should trade at $700 a share."
Apple share price has taken a dive of late, after the absence of new products releases but rose 4.75% today after Icahan's bold tweets.