The Princess was inspired to reach out to 12-year-old Mya Brower after she and her father Justin were featured in a BBC news story about scars being a sign of mental and physical strength.
Mya had Chiari decompression surgery at age 8 which left a long scar down the back of her neck.
Her dad was heartbroken to hear his little girl call her scar "ugly", and shared a photo of Mya's neck on Twitter in a bid to show her that people think scars are "badass".
The tweet quickly racked up 229,000 favourites while almost 75,000 users shared messages of support.
Eugenie, 28, posted a screenshot of the article to her Instagram story calling it "inspiring" and thanked the Brower's for sharing their personal situation, adding: "As Mya said, a scar makes you who you are."
The newly married Princess, who underwent corrective spinal surgery for scoliosis aged 12, is an advocate of body positivity and proudly showcased her own back scar on her wedding day to Jack Brooksbank last October.
Eugenie opted for a custom designed Peter Piloto gown with a dipped back to convey her powerful message by highlighting the childhood scar that stretches from the top of her neck to her shoulder blades.
The daughter of Prince Andrew and Sarah Ferguson also wore her hair in a chic up do to reveal every inch of the mark.
Speaking about her sartorial statement, Princess Eugenie told Harper's Bazaar: "[It's] a lovely way to honour the people who looked after me and a way of standing up for young people who also go through this.
"I think you can change the way beauty is, and you can show people your scars and I think it's really special to stand up for that."