Sunderland chief executive Margaret Byrne has resigned with immediate effect in the wake of Adam Johnson's sex offence convictions.
Byrne said in a statement: "I recognise that, as CEO, my involvement with Mr Johnson and the decision to allow him to continue to represent Sunderland was a serious mistake."
Pressure has been growing on Byrne ever since Johnson claimed during his Crown Court trial that he had made full and frank admissions to the club and she had all the messages exchanged and transcripts from police interviews.
Sunderland initially suspended Johnson for a fortnight in March last year, but then allowed him back into the squad as the club fought relegation, and he was able to make a further 28 appearances.
But Sunderland have now acknowledged that the decision was wrong to let Johnson play again and the board have accepted Byrne's resignation.
A club statement from Sunderland AFC read: "The Board of Sunderland AFC has today accepted the resignation of Margaret Byrne.
"Margaret, in her role as CEO, was responsible for the running of the club. She was also accountable for the actions taken by the club in relation to Mr. Johnson.
"Sunderland AFC acknowledges that Margaret's intentions have always been to act in the best interests of the club, however it has become clear through our own internal investigations that in this instance decisions have been taken by Margaret in error.
"Whilst swift and decisive action was taken to terminate Mr. Johnson’s employment upon his guilty plea, decisions taken prior to this, including the decision not to suspend him for a second time pending the outcome of the trial, were wrong.
"In light of what has been acknowledged by Margaret as a serious error of judgment on her part, we have undertaken a full review of the club’s decision-making processes to ensure that there can be no such mistakes in the future.
"Throughout this deeply regretful situation, we recognise that one devoted young fan and her family have been very badly let down, first and foremost by Mr. Johnson and his despicable actions, but also by the club they support. We are so very sorry for this.
"Mr. Johnson lied to the club; he also lied to our fans and they have every right to feel aggrieved by this. Lessons have been learned and we hope that the club and its fans can move forward from this together."
Byrne spent last week in Portugal, but returned to the UK over the weekend, with her position then looking untenable, amidst growing media pressure.
Her departure brings to an eight-year association with Sunderland after she was appointed club secretary in 2007, before becoming chief executive four years later.