Why? Because it turns out the Keeping Up With the Kardashian's star was obligated to ditch her summery blond 'do for her Vogue magazine cover!
The 33-year-old stunner's hair colorist, Tracy Cunningham, took to Instagram to caption one of the iconic photos shot by Annie Leibovitz while dishing the deets of Kim's hair makeover in preparation for her Vogue cover with fiancé Kanye West.
"Now I know why @kimkardashian needed to go back to her natural #brunette! She told me it was top secret and I would know soon enough! So cool @voguemagazine #ilovemyjob #kimkardashian#kanyewest #redkenready Thank God for #shadeseq(The color that thinks its a conditioner) for Shiny,Silky and Healthy Hair!," she wrote.
The reasoning behind Kim's dye job was one of the many secrets the mother of one kept from her family, friends and fans as Kimye went on a covert mission to keep the cover under wraps.
The fashionista appeared on Late Night with Seth Meyers last night where she admitted that it was a "top-secret mission" to disguise the photo shoot from her family, particularly her sisters, although the surprise ended up being a success.
"They were a little suspicious," Kim admitted, "but I just said Kanye was shooting something at my mom's house and it was really private, and just kind of blamed it on him."
She insisted, laughing, "I don't keep secrets!"
Well, except for this one.
But not every Kardashian tress transformation is a top secret mission, as Khloe Kardashian recently look a page from her sister's book and lightened her locks as well, Instagramming a pic while writing, "Thanks @anjabee for giving me my blonde bitchy babe hair! #RamirezTran ✌️ @jenatkin your moral support was much appreciated"
The 29-year-old beauty's colorist Anja Burton of Ramirez Tran Salon tells E! News she colored the E! star's hair on Friday.
"She was at the salon for a few hours. She's getting ready for vacation and wanted summer hair," Burton tells us. "I highlighted her hair to lighten and brighten her hair up. We did find some fun inspiration photos."
And girl looks great!
—Additional reporting by Lindsey Caldwell
Do you prefer Kim's dark 'do or Khloé's light locks? Tell us in the comments!