Ozzy Osbourne cheated on his wife Sharon Osbourne with their children's nanny, the night their son JACK was born.

In her forthcoming autobiography Extreme, Sharon reveals a drunken Ozzy 'celebrated' the birth of Jack in 1985 by jumping into bed with their child care assistant.

Sharon says, "Ozzy was loaded when he got to the hospital. Then he collapsed and went home.

"My assistant popped in to see if he was OK and found him in bed with the nanny. She wasn't a beautiful blonde, she was an ugly old cow.

"Ozzy was a raging drunk. I don't know if he actually got it up."

Despite Ozzy's infidelity, Sharon has forgiven his bad behaviour, blaming it on his drug and alcohol abuse.

She explains, "I forgave him. If my husband was sober and having a mad, passionate affair, that would be different... I have been faithful in my marriage."