Jack Osbourne diagnosed with multiple sclerosis, Kelly Osbourne tweets for brother's support

Jack Osbourne has been diagnosed with multiple sclerosis.

The 26-year-old told People magazine he learned of his illness two weeks after the birth of his daughter Pearl with his fiancée Lisa Stelly.

The disease affects the central nervous system and can cause problems with muscle control and strength.

Jack's sister Kelly tweeted her support, saying "please support my brother in not only his bravery but honesty!"