The 32-year-old British television personality wrote in her memoir, There is No [Expletive] Secret: Letters from a [Expletive], that Ozzy overdosed on drugs in 2002 while accompanying Sharon to the hospital amid her stage-three cancer battle.
"[One day] Mum had a seizure," Kelly recounted, according to People. "I call for an ambulance and together with her idiot nurse, we got Mum stabilized."
"I ran downstairs to get Dad from his room. Dad was there in his boxers, and I watched him scoop his hand into a bowl of pills, swallow a handful of something and wash it down with vodka, like it was water and he was dying of thirst. I didn't know what to do," she admitted.
"[In the ambulance], he leaned over to put his hand out to see if Mum was breathing," the star said. "Then he passed out with his hand over her mouth, and it looked like he was trying to kill her."
Kelly said EMTs agreed not to call police about Ozzy's overdose, but insisted on "rushing [him] into detox" once they reached the hospital. Kelly was left running back and forth between her parents upon arrival.
"[I was going] from the room where my mother was recovering from a seizure to the room where my father was being treated for a drug overdose and alcohol poisoning," she said, according to Page Six.
Sharon ultimately recovered from the seizure and the colorectal cancer, but had a double mastectomy in 2012 after learning she was at risk for breast cancer. Ozzy, who struggled with addiction issues for years, said in May that he's sober and hasn't "touched drugs or alcohol" for over three years.