Ozzy Osbourne has vowed to get clean and sober for his daughter Kelly, according to a source.
The 64-year-old rocker - who recently admitted he relapsed and has been addicted to prescription drugs for the past 18 months - promised the Fashion Police co-host that he would get his life back on track before she tied the knot with vegetarian chef Matthew Mosshart so he could walk her down the aisle, a source close to the 28-year-old star told gossip website RadarOnline.
"Kelly's using a little blackmail to help her father get clean sooner rather than later. She knows he has to want it, but she thinks a little tough-love encouragement can't hurt," the source said.
"Kelly went right for daddy's heart - she made it clear that she needed him to be present when he walked his little girl down the aisle.
"Ozzy would never ruin her big day, so he promised Kelly that he would get it together way before her wedding to Matthew.
"Ozzy knows better than anyone that he can't sober up for anyone except himself.
"Kelly even threatened that if he wasn't coherent by the time of the wedding that she would have her brother Jack give her away."
Sources have said that Kelly and Matthew, who met at Kate Moss's wedding to Jamie Hince in July 2011, got engaged before Christmas.
But Kelly is adamant her man has not popped the question.
Speaking on The Kyle & Jackie O Show on Australian station 2DayFM, she said: "I'm not telling you guys anything. When I have a ring on my finger, then you'll know I'm engaged."
Kelly's mother, Sharon, 60, recently admitted that she "didn't realise the extent" of her Ozzy's problems with prescription drugs.
However, the mother-of-three insisted she has no plans to walk away from their marriage.
"We're not getting divorced. However, am I happy? No. Am I upset? Yes, I am. I'm devastated right now," Sharon said.
"It's a disease that not only hurts the person that has the disease but it hurts the family. It hurts people who love you.
"We're dealing with it. We've dealt with worse. We're dealing with it and this too shall pass."