M&A lawyer Stephen Fraidin is leaving billionaire Bill Ackman’s Pershing Square Capital Management for Cadwalader, the firm announced Monday.

Fraidin, who has served on Pershing Square’s board of advisors since its founding in 2004, joined the fund as vice chairman in 2015.

“I was having a really good time at Pershing Square, and Bill Ackman and I are very close,” Fraidin told Bloomberg Law. “But it turned out that what I really love doing is practicing M&A law and advising boards on challenging corporate governance issues. There really was very little opportunity to do that kind of work at Pershing Square.”

As a partner in Cadwalader’s New York office, Fraidin will dive back into those kinds of matters, which he previously worked on as a partner at Fried Frank and Kirkland & Ellis.

Cadwalader is one of Pershing Square’s principal outside firms, according to Fraidin, who said his familiarity with the firm made his decision to move there a “clear choice.”

“Cadwalader clearly and unambiguously wants me to do what I want to do, which is roll up my sleeves and work on M&A matters and major corporate governance matters,” he said. “That’s exactly what they want me to do.”

Among many blockbuster deals, Fraidin has represented companies like 3G Capital in the $28 billion acquisition of H.J. Heinz Company, Burger King Worldwide Inc. in its $11.4 billion acquisition of Tim Hortons Inc., and Pershing Square and Valeant Pharmaceuticals in their unsuccessful takeover bid for Allergan.

Pershing Square announced Fraidin’s departure in a quarterly earnings report and call last month.

“Steve has been a brilliant advisor and partner to Pershing Square, and we look forward to continuing to benefit from his wise counsel,” Ackman wrote in his letter to investors.

Fraidin will remain on the Pershing Square advisory board while at Cadwalader.