Jack Osbourne and fiancée Lisa Stelly expecting first baby

Jack Osbourne has revealed that he and fiancée Lisa Stelly are expecting their first child.

The 25-year-old announced the news during an interview on Piers Morgan Tonight on Tuesday, during which he admitted to having mixed feelings about his impending fatherhood.

"I'm excited. I'm a little nervous, but I'm excited," Osbourne said. "It's gonna be fun. I'm not going to do a reality show, though!"

He and Stelly announced their engagement last month after dating for less than a year.

When Morgan asked Osbourne's father Ozzy how he felt about becoming a grandfather again, he added: "I'm in shock. I think it's fabulous."

He is a grandfather of four through children Jessica and Louis from his first marriage to Thelma Riley.

Jack's mother Sharon also expressed her happiness, saying that she had "always wanted to be a grandma".

Jack recently slammed "assholes" in the press for intruding upon Stelly's privacy and calling for the media to approach the situation in "the right way".

Jack's sister Kelly has said that she is "unbelievably proud" of her brother for proposing to Stelly.

She later described Stelly as "awesome", confessing that Stelly is the only one of Jack's girlfriends that she has ever approved of.

Watch a clip of Jack, Ozzy and Sharon Osbourne on Piers Morgan Tonight below: