Jack Osbourne says his mother Sharon "falls apart" when she's given bad news.
The 28-year-old star - who was diagnosed with multiple sclerosis last year - admitted he had to keep secrets because of his mum's recent marital problems with her husband Ozzy.
He told the Sunday Mirror newspaper: "I actually ended up keeping a lot of my stuff secret from my mum as she was such an emotional basket case if I did.
"She a tiger mum, but that only works when she's able to function. If I ever tell her any bad news, she falls apart."
The reality TV star - whose wife Lisa Stelly gave birth to their first child just before his diagnosis last summer- didn't want to discuss his parents' relationship problems in too much detail, but he admitted he can't imagine them apart.
He added: "It has been a very difficult year. I don't want to go into details about what my parents went through because that's their business.
"It is hard to imagine my parents not being together."
Jack explained the family are stronger now, and his illness helped them address their priorities.
He said: "Years like this can either tear you apart or make you stronger - and with the Osbournes, it's made us even stronger.
"My illness has made us realize how fragile we all are and given us some perspective. When we're together, we are a tribe, it's business as usual - it's crazy."