Jack Osbourne diagnosed with multiple sclerosis

The joy of becoming a new father has been tarnished for Jack Osbourne and his famous family, with news the 26-year-old has multiple sclerosis (M.S.). The diagnosis was made when Jack lost 60 percent of the vision in his right eye, just weeks after he and fiancée Lisa Stelly welcomed daughter Pearl into the world on April 24. "I was just angry and frustrated and kept thinking, 'Why now?'" he told People. "I've got a family and that's what's supposed to be the most important thing." Multiple sclerosis affects the brain's ability to communicate with the spinal cord, and can lead to blindness and cognitive disability. But, with his trademark pluck intact, Jack went on to say that "Adapt and overcome" would be his new motto. Fans rushed to express their condolences via Twitter, but the star stayed mostly quiet -- though he did tweet that he enjoyed his "best" Father's Day ever.