Billionaire Carl Icahn tweeted today that he purchased a “large position” in Apple after chatting with chief executive Tim Cook today.

“We appreciate the interest and investment of all our shareholders,” an Apple spokesperson told VentureBeat in an email. “Tim had a very positive conversation with Mr. Icahn today.”

Icahn believes that Apple is “extremely undervalued,” according to his tweets, and has made a significant investment in the company. He did not disclose the amount of the investment. Furthermore, he said that he is encouraging Cook to undergo a “larger buyback [that] should be done now.”

In April, Apple announced that it plans to return $60 billion to its shareholders as a part of a share repurchasing program. It originally started out as a smaller $10 billion plan, but Apple soon added the extra $50 billion.

Apple’s stock was trending downward until the beginning of August. It is now sitting at $493 a share, up five percent on Icahn’s news. This could have been because of its relatively lackluster Worldwide Developers Conference, which some criticized as missing the “wow factor.”

Icahn is otherwise busy with his attempt to take over beleaguered Dell, but he doesn’t plan on letting that distract him. He says that he will speak with Cook again “shortly.”