Jack Osbourne Reveals He’s Been Diagnosed with Multiple Sclerosis

New dad Jack Osbourne has been diagnosed with multiple sclerosis, an autoimmune disease that affects the brain and spinal cord.

The 26-year-old son of rocker Ozzy Osbourne and America’s Got Talent judge Sharon Osbourne was dealt the health blow just two weeks after he and his fiancée welcomed their first child, daughter Pearl Clementine.

“I was just angry and frustrated and kept thinking, ‘Why now?’ ” Jack told PEOPLE.

“I’ve got a family and that’s what’s supposed to be the most important thing.”

Multiple sclerosis, also known as MS, is an inflammatory disease that affects the ability of nerve cells in the brain and spinal cord to communicate with each other effectively. It can cause problems with muscle control and strength, vision, balance, feeling and thinking.

Millions of people worldwide suffer from MS, including a number of celebrities: Those who’ve battled the disease include comedian Richard Pryor, Emmy award-winning talk show host Montel Williams and Teri Garr, the actress best known for her Academy Award-nominated role in Tootsie, opposite Dustin Hoffman.

Others who have opened up about their struggles with the illness include Fox News anchor Neil Cavuto and Anne Romney, the wife of Presidential candidate Mitt Romney.