The author, 35, was the victim of an acid attack organised by her ex-boyfriend, and she suffered life-changing facial scars following the incident.
Taking to Instagram, she captioned the photo: “@princesseugenie looked stunning today but she also has helped so many people by showing her scar and for this I love her!
“This is quite a break through and refreshing in an edited world. Thank you!!!!! #change #scars.”
The Queen’s grandaughter underwent major surgery on her back to treat a curvature of the spine at the age of 12.
Princess Eugenie wore a dress which highlighted her scar in order to “honour the people” who cared for her during her surgery.
Speaking to ITV’s This Morning Princess, she said: “I had an operation when I was 12 on my back, and you’ll see on Friday, but 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.”
Fans appreciated Princess Eugenie’s body confidence as they flooded Katie’s Instagram account with praise for her.
One person said: “Very admirable to embrace this on such a big day.”
Another commented: “My 13-year-old daughter gets this surgery in seven weeks and this picture is such an inspiration to her!”
A third person replied: “That’s amazing @katiepiper even more amazing I did not even notice. Maybe we are learning to look over things.
“By the way we all think you are amazing.”
Scoliosis is a condition that affects the spinal cord when the spine curves to the side or is twisted.
According to Scoliosis Association UK, the condition affects three to four children per 1,000.
Princess Eugenie tied the knot with her long-term beau Jack at St George’s Chapel in Windsor earlier today.
Many A-list faces attended the ceremony including Robbie Williams, Ayda Field, Naomi Campbell and Kate Moss.
Katie Piper will be turning her attention to game time on the ballroom dancefloor when she and professional dance partner Gorka Marquez perform tomorrow night.
Strictly Come Dancing 2018 continues tomorrow on BBC One at 6.40pm