The former reality star and son of Ozzy and Sharon Osbourne revealed his health crisis in an interview with People released Sunday. He told the magazine he was angry and frustrated when he found out, and he's concerned about his family.
Osbourne and his fiancé Lisa Stelly had daughter Pearl in April.
Multiple sclerosis attacks the brain and spinal cord, and can cause somewhat mild problems or serious disability, such as paralysis.
Jack Osbourne gained fame as a teen when his heavy metal father and his mother allowed the family to be profiled in the MTV reality show "The Osbournes."