Sunderland chief executive Margaret Byrne has resigned in the wake of the Adam Johnson child sex abuse case admitting "a serious error of judgement".
Johnson was suspended a year ago then allowed back into the team and played for the Premier League strugglers until his trial when he pleaded guilty to grooming and a sexual activity with a child.
Pressure was put on the club after Johnson's legal team told Bradford Crown Court the club was aware that he had told police he kissed the girl.
The club had stated he had told them he intended to deny all the charges against him.
Ms Byrne said in a statement: "Contrary to what has been suggested, I did not understand that Mr Johnson intended to change his plea at trial or at all.
"I was astounded when he did plead guilty.
"I accept that Mr Johnson should not have been permitted to play again, irrespective of what he was going to plead.
"It was a serious error of judgement and I accept full responsibility for this."
The chief executive said she recommended to the Sunderland board that Johnson should be allowed to play on last year because he was fighting the charges and was "innocent until proven guilty".
She said: "Mr Johnson's victim has endured a terrible ordeal and for that I am truly sorry.
"At no time was the failure to suspend him again intended to cause any harm or distress to her or her family."
Stepping down after nine years with the Wearsiders, she said: "I recognise that, as CEO, my involvement with Mr Johnson and the decision to allow him to continue to represent the club was a serious mistake.
"I sincerely regret that this error has impacted on the victim, the club, its supporters and all those affected in such a devastating manner."
She was hurt by the criticism levelled at the club, saying: "To this end and for the long-term good of the club and its staff, I have stepped down as CEO with immediate effect."
In a statement, she explained her role after Johnson was arrested last March by police investigating allegations that he groomed and had sexual activity with a 15-year-old fan.
Ms Byrne said she first met police while he was still in custody.
She explained: "At this time they outlined the nature of the allegations but did not go into detail as he had not been interviewed or charged at this point."
A decision was made to suspend him, with the agreement of the board and chairman.
But, controversially, this was lifted after two weeks. She said the reversal came "after the club's position was considered with external legal advisers and the PFA".
She added: "Mr Johnson had still not been charged with any offence."
Under Dutch veteran manager Dick Advocaat, Sunderland managed to just avoid relegation from the Premier League.
Ms Bryne, a lawyer, said Johnson asked for advice about legal representation and she arranged for him to meet Orlando Pownall QC.
She said the player's father sent her some documents to be forwarded to the barrister.
"I did not examine the contents of these documents in any detail," she said.
She attended part of the introductory meeting with the eminent QC on May 4.
She said: "After this meeting, Mr Pownall sent me a note to forward to Mr Johnson which recorded , amongst other things, that Mr Johnson had kissed the victim and communicated with her.
"I did not share this information with anybody including the board of Sunderland AFC.
"In the following days, Mr Johnson engaged Mr Pownall and changed his legal team and he confirmed to me that he was intending to defend each charge.
"He told me that he was confident of a successful outcome."
The chief executive did not meet Mr Pownall again and said she played no role in the "plea decisions" his legal team made.
She said the board knew the broad nature of the allegations but not the detail that she was "privy to".
She added: "Mr Johnson remained innocent until proven guilty and I was concerned that any action taken by the club against him may be misinterpreted as a judgment on the club's part as to his guilt at a time when he steadfastly maintained his determination to plead not guilty and fight the charges.
"On that basis I recommended to the Board that Mr Johnson should be allowed to play for the club, pending trial."