Mike Anderson, the managing director of Metro, is expected to fill the vacant post while continuing in a role at the morning freesheet.
An Associated spokeswoman said: "I understand that Sally has resigned. I don't know who has taken over."
News of de la Bedoyere's departure comes amid reports that sales of the paper slipped 3% year on year for the January to June period.
The latest upheaval is one of a number of recent upsets at the paper, which has seen a string of staff leave since Veronica Wadley took over as editor.
Earlier this week, former Marie Claire editor Liz Jones was appointed editor of the Evening Standard's Life & Style section, replacing Jeremy Langmead who quit the post to become editor-in-chief of IPC Media's style bible Wallpaper.
It has also been reported that art critic and Evening Standard columnist Brian Sewell is unhappy at the newspaper, as well as other staff.
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