William Doyle is leaving Pershing Square.
Pershing just posted a letter to shareholders running through the fund's investments, revealing that Doyle would be leaving.
Doyle, who attended Harvard Business School with Pershing founder Bill Ackman, played a key role in the fund's investment in Valeant.
He was involved in introducing Ackman to Michael Pearson, the then CEO of Valeant, according to The New York Times. Doyle knew Pearson socially.
It was at that point that Ackman and Pearson started working on a plan to have Valeant buy Allergan, an effort that was eventually thwarted. Pershing later bought in to Valeant.
That investment has proven disastrous. Pershing's position in Valeant fell 16.2% in the first three months of 2015, adding to a sharp decline through 2015. The company has a new CEO, a new look board, and is under investigation in four states. 
The Pershing letter on Wednesday said:
Bill Doyle originally joined Pershing Square on a part-time basis as a Senior Advisor in September 2013. At that time he was still actively involved with several of his venture portfolio companies, most notably as Chairman of Novocure, a privately held cancer therapy company that treats Glioblastoma, a cancer of the brain. In October 2014, Bill became an official member of the investment team. A year later, on October 2, 2015, Novocure completed its public offering. Bill has recently assumed the Executive Chairman role at Novocure. The demands of overseeing Novocure and managing its relationship with its shareholders and other stakeholders have made it infeasible for Bill to continue as a member of the investment team. As a result, Bill will be leaving Pershing Square Capital Management and, in addition to Novocure, will be working part-time at Table Management, an entity which oversees private investments for my family.
Pershing said in late April that Doyle would leave the board of Zoetis, an animal-healthcare company and a Pershing investment. His term expires on Thursday. Pershing cut its stake in Zoetis earlier this week.
The departure of Doyle, who worked at Johnson & Johnson and his own healthcare venture-capital firm before joining Pershing, follows that of another Ackman lieutenant: Paul Hilal.
Ackman announced in January that Hilal, a partner, would leave the activist hedge fund to launch his own venture.
Business Insider reported earlier this week on some of the emails between Ackman, Pearson, and others that were released by the US Senate.
On Monday, Valeant's new CEO, Joe Papa, delivered his first interview since taking over.
Papa's only a week into his new gig, and he said that his first priority is to "re-recruit" Valeant employees.

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