Jack Osbourne has admitted that he worries about his mother's hectic workload.

The 20-year-old instructed Sharon, who has battled colon cancer and bulimia, to take frequent rests while filming for The X Factor and The Sharon Osbourne Show.

"Of course I still worry about my mum," Jack told The Mirror. "Before she left for London I told her not to work too hard and rest a lot. Then I heard she'd been out every night.

"There is no half-assed Sharon Osbourne. But I can't remember the last time she was sick so my fear is becoming slowly irrational."