Francine Cornell met the singer during last year's Boyzone tour and left her boyfriend of three years Nick Robbins in October, reports the Sunday Mirror.
Robbins's father, Royston, said: "Nick had remarked to me and to his brother Andrew that she was working with Ronan Keating and that she seemed to be always receiving text messages from him.
“He didn’t seem to be jealous about it, he just thought there were rather a lot of them. The next thing I heard was that she had told him, in front of all their friends on holiday, that she wanted to end things. It was October 25, Nick’s 30th birthday."
A source claimed the affair lasted for seven months, adding that the "besotted" Keating tried to end it a number of times but found that he "can't stay away from her".
"He can't hide the fact he fell in love with her. He's obsessed with her – besotted," the insider claimed. Guilt-ridden Keating is expected to return to his family home tomorrow in an attempt to reconcile with his wife of 12 years, Yvonne.