JPMorgan Chase Chief Operating Officer Matt Zames is leaving the firm, CEO Jamie Dimon said in a memo Thursday.

“Our colleague, Matt Zames, Chief Operating Officer, recently informed me of his decision to leave our firm following 13 years of outstanding service,” Dimon said in the memo.

Zames was considered by many to be a potential successor to Jamie Dimon when the CEO and Chairman eventually decided to step down. The Wall Street Journal in 2014 called him a “potential favorite” for the position because his work in helping Dimon navigate the financial crisis.

Dimon said in the memo Zames “was an integral part of the team that helped manage the firm successfully through the financial crisis.”

The memo did not make it immediately clear that there would be a replacement for Zames, instead laying out a new organizational structure dividing up the COO’s roles.

JPMorgan did not immediately return a CNBC call for comment.

The memo said Zames “will be here over the coming weeks to help ensure a smooth transition of his responsibilities.” It does not mention any plans beyond that for Zames.

— CNBC’s Wilfred Frost and John Melloy contributed to this report.