Fleming had long been considered as a potential heir apparent to CEO James Gorman, but Kelleher's appointment cast his ascendance into doubt.

So he left, and in typical Wall Street fashion, CEO James Gorman vaguely wrote a memo saying Fleming would be pursing other opportunities.

Fleming also wrote a memo that went only to members of his team reminding them to continue doing great work regardless of his departure.

Here's the full memo: 

The new year always brings change and new challenges and, for me, those challenges will be on the horizon beyond Morgan Stanley. I want to take this opportunity to tell you how proud I am to have led this organization for the past five years, and to reflect on what we accomplished together.