THE clan behind the History Channel’s popular “Pawn Stars” is hiding a shameful family secret!

Joseph Harrison, the 51-year-old son of family patriarch Richard “The Old Man” Harrison, is reportedly a longtime member of a biker gang and has been charged with numerous felonies.

According to court documents obtained by The ENQUIRER, Joseph and other members of the notorious Vagos biker gang entered a couple’s home in July 1997 and demanded money, drugs and personal possessions. Joseph then battered a man while another gang member ripped a phone out of the wall and grabbed one of the couple’s leather jackets, the documents said.

Harrison pleaded guilty in 1999 to extortion. He was sentenced to between four and 10 years in prison, but that was suspended and he wound up with just two years’ probation.

Joseph is still affiliated with the violent gang and recently tricked his father into hosting a so-called “Valentine’s Defense Party” that helped raise money for the biker gang’s court costs and attorney fees, revealed the source.

The event infuriated Joseph’s brother Rick – who with their father founded the famed Gold & Silver Pawn in Las Vegas, according to the source. “Rick hit the roof,” said the source. “He was fit to be tied that Joseph would use their 73-year-old dad to be an unwitting accomplice in his plan to raise money for his gang.

“Joseph is the black sheep of the family. He’ll never change, and they want nothing more to do with him!”