Jack Osbourne attends the Activision's Ultimate 'Call of Duty XP' Fan Experience at The Stages at Playa Vista on September 3, 2011 in Los Angeles, California. Credit: Frederick M. Brown/Getty Images

Sad news for new dad Jack Osbourne.

Just two weeks after welcoming his first baby, a daughter named Pearl, with his fiancee Lisa Stelly, Ozzy Osbourne's 26-year-old son learned he was diagnosed with multiple sclerosis, a source confirms to Us Weekly.

"He knew something was wrong for awhile," the source says of the former Osbournes star turned filmmaker. "Everyone is sad, but he is being strong about it."

A disease that affects the central nervous system -- the brain and spinal cord -- MS can cause problems with muscle control, vision, balance, and thinking.

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

The chronic disease can result in loss of vision or severe paralysis. The progression of MS is unpredictable and symptoms vary from one person to another.

According to the National MS Society, approximately 400,000 Americans suffer from the disease, with 200 more being diagnosed every week.

Talk show host Montel Williams went public with his diagnosis in 1999 and in the years since, started a foundation that has distributed $1.5 million in grant money to fund research efforts.

Osbourne and fiancee Stelly's little girl Pearl was born in late April, weighing 8 lbs. and 6 oz. He and aspiring actress Stelly announced their engagement in September of last year.