Though she might be a radiant reality TV star now, with her own range of false eyelashes and a popular style and beauty blog, Millie has revealed that her looks - particularly her skin - used to get her down and cause people to tease her.
Speaking to Fabulous magazine, the 24-year-old explained that she hasn't always been so polished and fashionable.
"I was bullied to the point where I wouldn't want to go to school," she said. "I was skinny, had glasses, wore braces to realign my jaw, had full-on yellow hair after a home dye job and really bad acne all over my forehead.
"I thought it would never go away. I remember trying to scrub my spots off with St Ives Apricot Scrub and ending up as this red raw mess. Then I'd try and cover it up with loads of make-up."
Millie attended a boarding school, so it was even harder to escape the jibes from her fellow classmates. She also added that feeling down about how she looked didn't help when it came to fancying boys.
"I had such a s**t time as a teenager and I know it can really get you down."
Well, the Chelsea star doesn't have to worry about "mean" men these days. Not only does she appear flawless on screen and feature on 'best dressed' lists frequently, she has also bagged herself a famous fiancé.
Millie is currently planning her wedding to rapper Professor Green and is thought to be leaving the cast of Made In Chelsea to focus on her life with him, after they get married in September.
She's even been accompanying her man to a number of his gigs over the last couple of months and has proved what a doting future-wife she is by nursing the injured rap star back to health in May when he was hit by a car.
Although Millie and Pro Green have revealed very few details about their big day, Millie is said to be working out to get rid of her "wobbly bits" ahead of the ceremony.
Are you surprised to hear Millie's story about her time an a teen? Let us know below, as the best comment from across the website each week wins £50!
Michelle Keegan, TOWIE, Lady Gaga: yesterday's headlines in pictures
Copyright: WENN Steve Searle