The chief executive of Barking, Redbridge and Havering NHS Trust has stepped down just a week after asking staff to come up with cost-cutting ideas to save£10m.
A statement from the trust said Mr Rees, who has been chief executive for four years, had decided that this was 'the right moment to move on'.
In light of the plan to achieve foundation trust status, 'there now needs to be a commitment over the next five years to drive further changes', it said.
Mr Rees is married to Rose Gibb, who has this week stood down as chief executive of Maidstone & Tunbridge Wells.
His departure came just a week after he sent a letter to staff saying they needed to take 'rapid and decisive action to generate fast cash recovery' to save£10m by March. A spokesman for the trust said a planned deficit of£14m by the end of the financial year was looking likely to be£34m.
Deputy chief executive Sue Barnett has taken over the role in the short-term. An interim replacement is expected to be announced shortly.