Jack Osbourne is fighting mad.

Days after his mother, Sharon Osbourne, quit America's Got Talent in protest of her son's axed appearance on NBC's upcoming series Stars Earn Stripes, the reality star is lashing out at the network arguing that he was indeed fired from the show following his multiple sclerosis diagnosis.

PHOTOS: Biggest reality TV bombshells ever

"NBC said they didn't fire me over my diagnosis? Bull-F--k----S--t," Jack, 26, tweeted, linking to a TMZ report that included a statement from NBC Chairman Bob Greenblatt to the contrary. "I took part in a 16 hour challenge over 30 miles with a 40 pound ruck [sack] on my back in January. I had MS then," says Jack, who was set to compete on the NBC series that features celebrities competing in military-style challenges. "Don't tell me [what] physically demanding is."

PHOTOS: Celeb health struggles

Speaking to the New York Post, Stars Earn Stripes producer David Hurwitz reasoned that Jack's appearance on the show was being considered, but no contract had been signed. "He was somebody we were in talks with," Hurwitz said, though Sharon, 59, was able to furnish emails with Hurwitz suggesting a verbal agreement that was quickly reneged after Jack went public with his MS diagnosis in June.

PHOTOS: Nasty celeb feuds

"Sharon has been a valuable part of the NBC family. We regret any misunderstanding and wish Jack well," an NBC rep told the Post Sunday of the AGT judge, who remains under contract with the network.

Stars Earn Stripes, featuring celebs including Drew Lachey and Dean Cain, premieres August 13.

This article originally appeared on Usmagazine.com: Jack Osbourne Bashes NBC for Firing Him Because of MS Diagnosis