Jack Osbourne

Jack Osbourne has been diagnosed with multiple sclerosis, People reports.

Osbourne, 26, learned of the shocking news just two weeks after he and fiancée Lisa Stelly welcomed their first child, daughter Pearl Clementine. "I was just angry and frustrated and kept thinking, 'Why now?' " Jack told the magazine. "I've got a family and that's what's supposed to be the most important thing."

It's a girl for Jack Osbourne and Lisa Stelly

Multiple Sclerosis affects the central nervous system — specifically the brain and the spiral cord — and can cause problems with muscle strength and control, balance, vision, feeling and thinking. However, the disease varies greatly from person to person — some people only experience minor issues while others are severely affected by the illness.

"Thank you all so much for the kind and inspirational words. It means a lot," Osbourne tweeted Monday, adding "adaptandovercome" as a hashtag.

Added his sister, Kelly: "Please support my brother [Jack] in not only his bravery but honesty! I love you so much Jack and I'm so proud of you!"

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Mom Sharon cried on Monday's episode of The Talk when talking about her son's diagnosis. "He's great, he's doing really, really good and I want to thank everyone for all their texts and goodwill and love they send to us," she said. "It's been amazing for Jack cause I really believe that vibes of prayer help."

Jack will appear on Wednesday's episode of the daytime talk show to discuss his disease.

Watch Sharon discuss Jack's diagnosis on The Talk: