The son of Ozzy Osbourne consulted doctors after experiencing eye problems when he was shooting scenes for a U.S. paranormal series in a cold lake, and he was diagnosed with the autoimmune disease just three weeks after he became a dad to daughter Pearl in April (12).
He tells Britain's Hello! magazine, "I was filming a TV show in Utah... and I had to do some scuba diving at night in a cold lake. When I came out, I had a headache and went back to the hotel to sleep.
"The next day the vision in my right eye started going in and out of focus. Later that evening, a black dot appeared in the same eye. When I woke up the next day the dot had turned into a cigar shape, and eventually it turned into a big blind spot in the middle of my eye.
"I went home and made an appointment with an eye doctor. By this point, I literally couldn't see anything out of my right eye; I just had a little bit of peripheral vision. The eye doctor said, 'There's nothing wrong with your eye. I'm going to send you over to Cedars-Sinai hospital (in Los Angeles)'. I think he knew what I had but he didn't want to say."
Jack also admits he has suffered symptoms of the condition, which affects the brain and central nervous system, in the past, adding, "The neurologist came to see me the next morning and asked me a lot of questions like, 'Have you ever had any paralysis, or numbness of the legs?' I said, 'Yes I have.' About two years ago my legs went numb for about two-and-a-half months. They were really sensitive to hot and cold... I just thought I had a pinched nerve."
The adventurous star is now facing having to cut back on his active lifestyle as a result of the diagnosis: "The doctors are telling me I can't overly exert myself, doing things like the marathon races that I love. I know it's probably horribly selfish of myself but I'm not really accepting that."