"I apologised to her for her treatment. It caused her genuine hurt and distress and she should not have been treated in that way. I also thanked her for her courage, her courage to come forward and complain. That is not easy but that is the only way that we can take action on these concerns."
Mr Rennie said employment law prevented him from divulging the details of the complaint.
Mr Sutton walked in to a press conference hand-in-hand with wife Jo Malcolm yesterday to announce his resignation, of his "own free choice", effective from January 31 next year.
"Hugs, jokes ... I do do those things, and I've hurt somebody with that behaviour and I'm very, very sorry about that," Mr Sutton said.
"But I am who I am. I have called women 'honey' and 'sweetie', and that is wrong. That's a sexist thing to do, and I'm really sorry."
His wife said the investigation process had been "hideous", and her husband's "hugs and jokes have been misinterpreted".