"I loved Lady Gaga. I totally believed in everything she stood for, until I realized she's a great big hypocrite," the 28-year-old "Fashion Police" host and July cover girl told Cosmo.
According to Zap2It, the feud started when Osbourne criticized Gaga for disappointing fans by ditching the Grammy Awards red carpet in 2012. Osbourne later said that Gaga's fans sent cruel messages to her about her weight.
"Don't say, 'When you see bullying, intervene,' while letting your fans send me death threats. If my fans did that, I would not stand for it," Osbourne said.
"You can say whatever you want with your millions of monsters," she added, in reference to Lady Gaga's affectionate name for her fans.
"I know the truth. You bells and whistles mean nothing to me. You're feeding on the freaks and geeks to further your career? Do you really care about the gay community? Because if you did, you'd stand up for it more than you do."
Osbourne also addressed her father's recent relapse, telling the magazine that she was proud of Ozzy for being honest about his substance abuse issues.
"I love and respect that he's honest enough to say, 'Yes, I did this. It was my fault.' He's a real man. Most people would hide, and he doesn't. It doesn't make me love him any less. It took a long time to get to that place, but I understand it now. And my mother does too."