Derek Llambias released a short statement after resigning as managing director at Newcastle United.
After Joe Kinnear's return as director of football - which has also left Alan Pardew's role as manager in doubt - Llambias has decided to resign with immediate effect.
It gives owner Mike Ashley another headache as he deals with the backlash against his decision to reappoint controversial Kinnear.
Llambias said: "I have had an incredible journey during my five years at the club, including some challenging times.
"I will reflect with great fondness on my time in the North East and, in me, Newcastle United have a lifelong supporter.
"I want to thank the staff for their hard work, our fans for their support of the club, and wish them all well for the future."