Kelly Osbourne and her boyfriend, Sid Wilson of Slipknot, had a "huge fight" about their baby's last name, as Kelly revealed on a recent episode of The Osbournes Podcast.

And it's something she "can never, ever forgive him for," she says.

Their son, the fifteen-month-old Sidney George Wilson IV, was named after his father, the longtime Slipknot turntablist. But, according to Kelly, there appears to be some confusion over whether little Sid is actually the fourth Sidney George Wilson. Not to mention her feelings over the baby not carrying the Osbourne surname.

"OK, this is personal, and I didn't expect to ever talk about this," Kelly tells her parents, Ozzy Osbourne and Sharon Osbourne, on the Feb. 20 The Osbournes episode.

READ MORE: Kelly Osbourne + Slipknot's Sid Wilson Share Christmas Photos With Baby Son

"The biggest fight me and my baby's father have ever, ever, ever had — and probably ever, ever will — was over naming our son," she says.

Kelly Osbourne's Baby's Last Name

Kelly explains, "I wanted our son to have both of our last names, and he wouldn't let me. And we had a huge fight. I feel that I was forced into doing something I didn't want to do. And I can never, ever forgive him for that. But we can move on."

Kelly Osbourne + Sid Wilson Christmas baby photo
Instagram: @kellyosbourne

By moving on, Kelly evidently means the couple will change their baby's last name to a hyphenated surname using both the Osbourne and Wilson names.

She says, "So right now my son doesn't have a double-barreled last name. But after lots of eye-opening conversations and some couples therapy, he has seen the light. And we are going to legally change our son's name to have both of our last names."

Kelly adds, "We both made our child, so they should have both of our last names. Not one is more important than the other. But you have to remember, Sid comes from a really traditional English family."

Sharon chimes in, "It's a very dated thing" — referring to the tradition of taking one's father's name — "a dated mentality."

"Don't even get me started, mom," Kelly responds. "Because it goes Sid's dad, then Sid and now our son. But Sid told me that his grandfather had the same name. But he didn't. His grandfather's name was Fred. Fred! So why is my son IV? My son should be III."

Watch the episode below at at 51:44.

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