Sharon Osbourne says her son's multiple sclerosis diagnosis ''scared the s**t'' out of her.

'The X Factor' judge and rock matriarch has opened up about the agony she endured last year when 27-year-old Jack discovered he had the debilitating disease, which affects the nervous system.

Sharon says her suspicions were raised when Jack - who has 17-month-old daughter, Pearl, with wife Lisa Stelly - began complaining he couldn't see out of his eye and was experiencing severe headaches.

In her new autobiography, 'Unbreakable', she recalls: ''I knew straight away it wasn't good. The symptoms sounded suspiciously familiar. In 1992 I'd done some research into multiple sclerosis when I thought Ozzy might have it.

''Jack went to see an eye specialist who said it was neurological. He went to the neurologist who said he needed an MRI scan. I went with him. I was watching the images of Jack's brain and the technician pointed to a couple of white spots. 'Looks like he may have had a stroke,' he said. It scared the s**t out of me.''

The 60-year-old star admits seeing Jack's struggle made her feel less sympathetic to her husband, Ozzy, 64, who had relapsed into drinking and drug abuse.

She candidly writes: ''I loved Ozzy as much as I had always done, but this time his illness seemed somehow pathetic ... This was about Jack, and I had no appetite for anyone else's problems.''