One month ago, when JPMorgan Chase's (JPM) top executives gathered for their annual day of investor presentations, Mike Cavanagh came back from lunch, stood at the front of the room and joked that he wanted a better spot in next year's lineup.

"Next year we will try again to not have the afternoon slot," said Cavanagh, then the co-head of JPMorgan's corporate and investment bank, and one of the leading candidates to eventually succeed Chief Executive Jamie Dimon.

So much for that. On Tuesday, news broke that Cavanagh is leaving JPMorgan Chase for the private-equity firm Carlyle Group, where he will become co-president and co-chief operating officer.

His departure is the latest in a long string of recent senior-level exits from the country's largest bank — and one of the most serious losses. It is also a setback for Dimon's efforts to solidify his leadership team and move on from the internal turmoil of the past two years. Since April 2012, when details about what became the London Whale affair began to emerge, JPMorgan has faced a crucible of regulatory settlements, shareholder scrutiny and regular reputational floggings. Last year the bank paid more than $20 billion to settle claims over everything from its mortgage operations to its energy trading and consumer debt collection activities.

Dimon has weathered most of the external scrutiny, and handily defeated a shareholder vote last year to strip him of his chairman's title. But the strain appears to be showing up on his team, several members of which have left for top roles at other financial and technology companies.

Cavanagh's departure seems like one of the most serious, to judge by Dimon's public reactions.

"This is a regrettable loss for our company, as Mike has been a part of the fabric of our organization for the last 14 years," Dimon said in an internal memo, praising his departing lieutenant as "an exceptional partner with great instincts, integrity and strategic thinking."

In a bank press release, Cavanagh said the decision to leave was a hard one.

"It was not without a lot of soul-searching that I decided it was time for me to take my career in a different direction," he said, adding that he "wouldn't have left for any company other than The Carlyle Group, a firm and a management team I have known for a long time."

His formal role at JPMorgan will be taken over by his current partner, Daniel Pinto, who will become the sole CEO of the corporate and investment bank. But his informal shoes will be harder to fill. Along with Chief Operating Officer Matt Zames, Cavanagh was considered one of the executives most likely to eventually replace Dimon, who is 58.

Cavanagh was also one of Dimon's remaining stalwarts after the past few years of senior-level departures and management reshuffles. Since the bank's $6 billion trading loss in London came to light, JPMorgan has lost or replaced executives including its chief financial officer, co-chief operating officer, chief risk officer, chief compliance officer, co-head of litigation, chief investment officer, chief information officer and head of consumer banking.

Last May, Dimon acknowledged that the bank has had "too much turnover," and executives in February expressed their hope for 2014 to be a year of transition to better times for JPMorgan.

"Our job is just to continue going forward and deal with these things," Dimon said towards the end of the investor presentations a month ago. "So I'm grateful we got some behind us, and we want them all behind us so we can build this franchise."

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