Bill Ackman isn't the only hedge fund manager who likely made big money on the Allergan deal.
Actavis announced on Monday that it will acquire Allergan for $66 billion, or $219 per share in cash and Actavis shares. The stock had been trading bear $110 earlier this year.
Allergan is one of the most widely held stocks by hedge funds. As of Sept. 30, some 19 percent of hedge funds owned it, according to an analysis of public holdings by data analysis company Symmetric.
The largest holder is Ackman's Pershing Square Capital Management, with $5.14 billion worth of shares (28.8 million) as of Sept. 30. The firm bought the stock at an average price of $127; at the current price, that means a more than $2 billion gain after a profit-sharing arrangement with Valeant. (Ackman had tried to buy Allergan by teaming up with Valeant earlier this year.)
Other top hedge fund holders including John Paulson's Paulson & Co., Dan Och's Och-Ziff Capital Management Group, Matthew Halbower's Pentwater Capital Management and private funds controlled by money management giant BlackRock.
Jeffrey Altman's Owl Creek Asset Management opened the largest new position in the third quarter, taking a $114 million stake. Hedge funds that got in earlier than most include Och-Ziff (2011) and Jacob Gottlieb's Visium Asset Management (2013).
The exact amount of money made at each of the firms is unclear. But Allergan stock was up about 5.25 percent as of early afternoon Monday; it was already up nearly 80 percent in 2014.
"Today's transaction provides Allergan stockholders with substantial and immediate value," Allergan chairman and CEO David Pyott said in a statement. Indeed, it probably is an understatement.