Kid Rock is to be a grandfather for the first time

According to the publication, 21-year-old Bobby's partner is already four months along and the couple will be welcoming a baby girl into the world.

The 43-year-old rocker - whose real name is Robert Ritchie - hasn't yet commented on the happy news.

The 'Born Free' star won a custody battle against Kelley in 2000, charging her $25 a week in child support and raising his son largely on his own.

And the singer - who was previously married to Pamela Anderson - has previously admitted to keeping his on stage persona separate from his family life.

He has said: "Make no mistake, Bob Ritchie's up early in the morning taking pictures of his son on the first day of his senior year. Kid Rock is passed out in a hotel room somewhere with four scantily clad women."

However, he has also confessed to refusing to hide the excesses of his rock'n'roll lifestyle from Bobby when he was young.

He said: "When Junior was young, it was Christmastime. I had a gig the night before, and I was s**t-faced, just beyond. Drugs and alcohol. I passed out in my bathroom, dead weight.

"My son comes in, he's like, 'Grandma, something's wrong with Dad!' So my mom tries to get me to make this big excuse up. 'Tell him you came home and you were tired and this that and the other.'

"I'm sitting there at breakfast and I say, 'Your dad got trashed last night.' I'm going to sit here and lie to this kid? He's like seven. I'm like, 'Big concert, party afterward, I drank too much and passed out. I'm not proud of it, but that's what happens when you do that.' "