Kelly Osbourne claims her father Ozzy overdosed when her mother Sharon had a seizure while battling cancer

Kelly wrote: "[One night] Mum had a seizure. I finally called for an ambulance, and together with the idiot nurse, we got Mum stabilised."

The 32-year-old star was terrified of how the Black Sabbath frontman would react when he heard Sharon had had a seizure.

She continued: "I had reason to be scared. Dad was there in his boxers, and I watched him scoop his hand into a bowl of pills, swallow a handful of something, and then wash it down with vodka, like it was water and he was dying of thirst.

"In the ambulance, Dad] leaned over to and put his hand out and see if Mum was breathing. Then he passed out with his hand over her mouth, and it looked like he was trying to kill her."

The medical team eventually got Ozzy off Sharon and wanted to call police but "took pity" on Kelly and agreed not to get in contact with law enforcement.

In an extract from her book, 'There Is No F***ing Secret: Letters From a Badass Bitch', obtained by People magazine, she wrote: "I was sobbing and shaking, scared out of my mind. and the EMTs took pity on me and decided not to call the police, but said that they were rushing Dad into detox as soon as we got to the hospital."

Kelly also candidly discussed her own drug addiction in the book, which came about as she had no way to "face her life" during the period when Sharon was ill and Ozzy was struggling with his demons.

She recalled: "I had to make phone calls, sign papers, talk to doctors, console family members, and, at 19, make adult decisions that would have been hard for someone three times my age.

"The only way I could even face my life was by opening that pill bottle, shaking out a few pills -- or a handful- into my palm, and throwing them down my throat."

The former reality TV star went to rehab multiple times and is now sober, and has previously spoken of how she takes "every day as it comes" in her recovery.

She previously said: "I have to take every day as it comes. This is a disease. I was born with it. I'll die with it.

"I just want to be happy. Anything is better than the way it was."