Margaret Byrne has announced her resignation as Sunderland chief executive with immediate effect.
Byrne's position at the Premier League club came under increasing pressure when it became apparent that the CEO knew parts of Adam Johnson's involvement with a 15-year-old girl.
Johnson was allowed to represent Sunderland despite the charges that were pressed against him, and Byrne has admitted that she made a "serious mistake" during the scandal.
"My involvement with Johnson and the decision to allow him to continue to represent Sunderland was a serious mistake," Byrne said in a statement.
Meanwhile, Sunderland have also released a statement of their own, saying: "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."
Johnson, 28, is facing up to 10 years in prison after being found guilty of one count of sexual activity with a girl aged 15. The sentencing is expected to take place in the next two weeks.