Sheffield Wednesday chairman Dave Allen has resigned from the board, reports BBC Radio Sheffield.
A brief statement on the club's website confirmed that he resigned as chairman and as a director with immediate effect at a board meeting on Friday.
Allen replaced Geoff Hulley as chairman in June 2003, and had been a director for three years before that.
Under his stewardship, the Owls won promotion to the Championship via the League One play-offs in 2005.
However, tensions have recently grown between Allen and fans' group Wednesdayite, which owns 10% of the club's shares.
He blamed Wednesdayite for refusing to sell their stake after a proposed takeover by former Everton director Paul Gregg fell through in July this year.
Allen said in a resignation statement that "this is a sad day for me".
But he insisted: "I just cannot come to terms with some of the unprofessional behaviour surrounding the business.
"The final straw that has broken the camel's back is to realise that confidential boardroom matters have been discussed with outside parties.
"It is just totally unacceptable. Enough is enough."