Middleton has a 3-inch-long scar on her left temple, just below her hairline. It first came to public attention back in 2011, when critics originally thought it was evidence of a wig extension gone wrong (though obviously, that's not the case, her hair is unnervingly perfect).
A palace spokesperson had to clarify what it was, saying only that Middleton got the scar during childhood.
"The scar is related to a childhood operation," the spokesman told E! News at the time.
To this day, the information related to her surgery is under wraps, with dueling sources contradicting each other over whether it was anything from "very serious operation" to a simple birthmark removal.
It's not really anyone's business anyway. But still, leave it to Kate to hide a childhood story in that famous hair of hers.
This article originally appeared on InStyle U.S.