Cole, 27, refused to give him any constructive criticism after his performance as she was upset about comments he had made to a journalist saying she was 'just a girl from a council estate who got lucky'.
Wagner reportedly tried to avoid the clash on-air by visiting her dressing room before the show but she refused to see him.
A friend said to UK newspaper The Sun: 'He knew she was livid about what he had said and came marching up to her dressing room demanding to see her. He was begging to be forgiven and given the chance to explain.
'But she was getting changed and didn't want to see him. He could have tried to make amends earlier - but for some reason he chose to try and tackle her minutes before the show. Maybe he had heard she was going to mention it on the show.'