Former "Osbournes" star Jack Osbourne has revealed that he's been diagnosed with multiple sclerosis. Osbourne, 26, discovered that he suffers from the central nervous system disease weeks after celebrating the birth of his daughter, Pearl Clementine, with [article id="1671790"]fiancée Lisa Stelly[/article] in April.

Osbourne told People magazine that the diagnosis shocked and angered him and has thrown him for a loop. "I was just angry and frustrated and kept thinking, 'Why now?'" he told the magazine. "I've got a family and that's what's supposed to be the most important thing."

It's unknown how the disease -- which impacts the central nervous system, including the brain and spinal cord, causing problems with muscle control and strength as well as vision and balance -- will impact Osbourne's health. The results vary widely from patient to patient, which some suffering only minor health problems and others become seriously debilitated.

Sister Kelly Osbourne tweeted about Jack on Sunday, writing, "Please support my brother @mrjacko in not only his bravery but honesty! I love you so much Jack & I'm so proud of you!"

Jack, who has struggled with addiction in the past, kept a stiff upper lip, tweeting on Sunday that, "This is the best father's day I've ever had! Hahaha." He followed by thanking those who have reached out to him, writing, "Thank you all so much for the kind and inspirational words. It means a lot."

please support my brother @mrjacko in not only his bravery but honesty! i love you so much jack & I'm so proud of you!people.com/people/article...

— Kelly Osbourne (@MissKellyO) June 17, 2012

Mother Sharon Osbourne spoke to Britain's Hello magazine, reportedly wondering if something she did may have contributed to her son's illness. "I keep thinking, 'what did I do wrong? What did I eat or drink when I was pregnant?' I feel like it's somehow my fault."

The mag also spoke to rock icon Ozzy, who wondered how his history of drug abuse didn't catch up with him before his son. "If it was me, you'd think: 'Ozzy had a reputation and it caught up with him,'" Ozzy said. "But Jack is such a good guy."

Jack said he's trying to keep a positive attitude about the diagnosis and is treating the disease using a combination of drugs, holistic therapies and lifestyle changes.