Sharon Osbourne has reportedly quit America's Got Talent in a dispute with network NBC over her son Jack.

The judge previously sparked rumours she was leaving the hit series after she tweeted fellow judge Howard Stern saying: "Money is not the reason I'm not returning" but she later tweeted she was just taking a break from the talent show.

Sharon has now told The New York Post she will not be returning to the judging panel, despite still being under contract, because the network dropped her 26-year-old son Jack from its new celebrity reality TV series Stars Earn Stripes after he was diagnosed with multiple sclerosis.

The 59-year-old TV star said: "I just can't be fake. It's discrimination, and it was badly handled."

"It's time to move on. They can't make me do something I don't want to do," she insisted. "All they can do is stop me from being a judge on another network for five years."

Sharon claims producers of Stars Earn Stripes - which sees celebrities compete against one another in military training exercises - fired Jack by e-mail two days before filming began, after he had gone public with his condition.

A representative for NBC said: "Sharon has been a valuable part of the NBC family. We regret any misunderstanding and wish Jack well."