New mom Constance Wu paid a virtual visit to “The Tonight Show Starring Jimmy Fallon” on Friday, and gushed about her baby daughter with boyfriend Ryan Kattner.

During the interview, the “Fresh Off the Boat” star discussed a very unique feature of her daughter’s anatomy. “I had a beautiful baby girl in August,” Wu said. “She’s the best, she’s the best. She has a full head of hair. She has a blue butt.”

Wu explained that she’s not exaggerating.

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“Yes, her butt is the colour blue,” she said. “There’s this thing, I had never heard of it before. But it’s called a Mongolian spot. Apparently, it happens in a lot of Asian babies, and my boyfriend and I are both Asian. And it’s where your butt is blue for like the first two years of your life, and then it just goes away.”

The Mongolian spot, notes WebMD, is more commonly known as congenital melanocytosis, described as “a very common condition in any part of the body of dark-skinned babies. The spots are flat, grey-blue in colour (almost looking like a bruise), and can be small or large. They are caused by some pigment that didn’t make it to the top layer when baby’s skin was being formed. They are harmless and usually fade away by school age.”

“Well, I just think it’s a very special thing, and it’s not something she gets to show off while she’s walking down the street,” Wu continued.

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“Not that she’s walking yet. But I thought I would just tell you about her little blue butt,” she added. “It’s very special.”

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Hollywood’s Baby Boom Continues