jack-ms-230.jpgJack Osbourne has been diagnosed with multiple sclerosis, an insider confirms to Us Weekly.

"Thank you all so much for the kind and inspirational words," Osbourne, 26, tweeted late Sunday. "It means a lot. #adaptandovercome."

A source tells the mag, "He knew something was wrong for awhile. Everyone is sad, but he is being strong about it."

The disease affects the central nervous system, and it can cause problems with muscle control, vision, balance, and thinking. MS is unpredictable and symptoms vary from person to person, and according to the National MS Society, approximately 400,000 Americans suffer from the disease, with 200 more being diagnosed each week.

This sad news comes just two weeks after Jack and fiancee Lisa Stelly welcomed their first child, a daughter named Pearl.