Sunderland chief executive Margaret Byrne has resigned in the wake of Adam Johnson's conviction on child sex offences.

Johnson was found guilty on one count of sexual activity with a 15-year-old girl last week and had already admitted to one less serious charge and grooming.

While Sunderland said it was shocked by Johnson changing his plea to guilty on the two lesser charges, questions lingered as to what the Premier League club knew following his first police interview in May 2015.

Johnson continued to play for the club up until he pleaded guilty in court and was subsequently sacked on February 11, but Durham Police claim Sunderland was made aware of the 28-year-old's crimes the previous year.

A club statement 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 judgement 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."