The 17-year-old has continued to deny rumours that she's had lip fillers since she showed off a fuller-pout last year.
In a new teaser clip for Keeping Up With The Kardashians, big sister Khloe, 30, urges her sister to come clean about having the injections.
During a red carpet appearance, Kylie is shocked when a reporter quizzes her about the rumoured surgery.
She tells Khloe: "No one's ever asked me about my lips. My heart literally dropped."
In the VT, Khloe explains: "Kylie decided to plump her lips, and I don't think there's anything wrong with that. I think if you've done something though, it is right to cop up to it.
"If you avoid a question, you're gonna look like a liar."
Another teaser shows Kylie finally making the admission. She says: "I have temporary lip fillers. It's just an insecurity of mine and it's what I wanted to do."
"I'm just not ready to talk to reporters about my lips yet, because everyone always picks us apart."
Earlier this year, Kylie insisted her plump lips were down to growing up and good make-up.
She told Cosmopolitan: "You guys have watched me grow up since I was 9. My face is going to get different. Now, I know how to do my make-up, contour and everything."