Hedge fund mogul William Ackman told investors they could see a $6 billion payday when he closes the chapter on Allergan Inc., his firm's biggest bet of 2014. One week after botox manufacturer Allergan agreed to sell itself to rival Actavis Plc., Ackman wrote in his quarterly investment letter that his Pershing Square Capital Management, the Botox-maker's biggest investor, still owns 26.6 million shares. A regulatory filing showed at the end of the third quarter Ackman's $18 billion fund owned 28.87 million Allergan shares. While this isn't the deal the activist investor originally wanted - he had been pushing since April for rival Valeant buy Allergan - it will be lucrative all the same. The letter also said, "If we hold the shares until transaction closure, we will receive $3.4 billion in cash and 9.81 million shares of Actavis worth $2.6 billion at current value."