The head of Morgan Stanley's most prized business is leaving the firm

Greg Fleming, the president of Morgan Stanley's wealth management business, is leaving the firm, according to a memo from CEO James Gorman seen by Business Insider.

Colm Kelleher, who is currently head of the firm's institutional and trading businesses, will become the sole president of the bank, including the wealth management division.

Fleming and Kelleher were both seen as potential successors to CEO James Gorman.

Fleming is leaving the firm "to pursue other opportunities," according to the memo.

Fleming joined Morgan Stanley in 2009 and oversaw a "transformation of the investment management business," according to the memo.

"Greg has been an asset to the entire Firm and to me personally," Gorman wrote.

More to come...