Carl Icahn Has Made Another $643 Million On His Forest Labs Stake Today

The $25 billion deal for drug-maker Actavis acquiring Forest Laboratories is another massive win for billionaire investor Carl Icahn.

"We were extremely pleased with the announcement this morning that Forest Labs is to be acquired by Actavis in a transaction that values Forest at approximately $89.48 per share," Icahn said in a statement.

According to Icahn's latest 13F filing, he held 30,662,005 shares of Forest Labs as of December 31, 2013.

Today, the stock has risen more than 29%, or about $21, putting the stock price at about $92.43 per share.

So in just today's trading session, Icahn has made an additional $643.9 million since the opening bell rang.

Overall, though, Bloomberg News' Miles Weiss estimates that he could make about $1.7 billion on this investment.