Fans were initially surprised to learn about the teen’s preferred name, which Nicole posted about publicly in her Jan. 12 Instagram post for Kate's 18th birthday. 

But as the Simple Life alum—who is also mom to son Sparrow, 16—told People in January, "She has her whole life.”

And as husband Joel later clarified, going by Kate was a decision that their daughter made for herself when she was quite young.

"She's been going by her middle name since she was in, like, first grade,” he explained on Bunnie Xo's Dumb Blonde podcast in March. “She chose it."

The Good Charlotte singer first learned about her decision during an open house at her school. 

"The teacher was like, 'Kate's doing great. She's so nice,'" Joel shared. "We're like, 'Who's Kate?' And they're like, 'Your daughter, Kate. That's what she said her name was.'"

"We went home. We're like, 'You go by Kate at school?'" Joel continued. "She goes, 'Yeah, I like it.' And we were like, 'OK, great.'"

In fact, their daughter’s name has even become a litmus test for how well someone knows her. 

"If you know her, you know she's Kate. People that don't know her would call her Harlow," the 47-year-old noted. "It's kind of smart, actually. She knows if someone called her Harlow, they don't really know her."

For more from Nicole and Joel over the years, keep reading.