The D&AD chief executive, Michael Hockney, has walked out on the charity after four years in the role, just three days before the start of its flagship Congress event.
Hockney's sudden departure comes amid rumours of a power struggle among senior executives at the not-for-profit organisation.
However, D&AD is downplaying any drama behind Hockney's exit, claiming that the former Butterfield Day Devito Hockney founder has been planning the move for several months.
The D&AD chairman, Anthony Simonds-Gooding, said: "Michael has worked tirelessly in his commitment to D&AD and has created a really competent team there."
He added: "It's in a very healthy place; membership has doubled and awards entries are on the up."
Hockney said: "I have enjoyed my time at D&AD and am proud of the achievements we have made. My plan is to take a mini sabbatical - I haven't had one in 35 years."
A source close to the charity said there were no immediate plans to replace Hockney.
Simonds-Gooding will assume day-to-day control of the organisation and will review the vacancy once the D&AD Congress has come to its conclusion.
Hockney joined D&AD in May 2003, replacing David Kester, who left after nine years to head the Design Council. Hockney started his career at JWT before moving to BMP to work on the launch of Channel 4. He later formed BDDH, before leaving in 1994 to head the auction house Christie's.
Under Hockney's charge, D&AD has gunned for global expansion in an attempt to challenge the Cannes Lions as the pre-eminent international advertising awards scheme.
The fourth annual D&AD Congress launches on 26 March. It brings together practitioners from various media for a series of lectures, exhibitions and the D&AD awards presentation in May.
- Perspective, page 19.