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She's a trooper!

Princess Eugenie has opened up about a difficult childhood memory. Now 21, the younger child of Prince Andrew and Sarah Ferguson underwent 8 hours of intense surgery at age 12 to repair a severe curvature of the spine (a.k.a. scoliosis).

Eight pins were placed in her back during the operation, leaving Eugenie in intensive care for three days, followed by six days in a wheelchair. The Princess looked back on the ordeal with London's Telegraph newspaper during a recent visit to London's Royal National Orthopaedic Hospital, where her own surgery took place.

"I've got the scar on my back," Eugenie said -- revealing the scar on her neck -- to the mother of a current 16-year-old patient undergoing scoliosis surgery.

Eugenie offered sympathy to a young patient. "It hurts so much, I was in so much pain," she said. "Get better!"

"[I've got] good memories coming back even though I'm slightly scared of hospitals," she told the paper, noting how grateful she was for the procedure.

"I wouldn't look the way I do," she added. "My back would be hunched over. I wouldn't be able to talk the way I do about it and help other children who come to me with the same problem."

Her scoliosis was discovered by accident -- when Princess Eugenie was getting a massage.

And she's thrilled to be a role model to kids undergoing the same procedure today. "It was a huge part of my life when I was 12 - so young. Children can see me and know that [the operation] works."