Sarah, Duchess of York wished she had bulimia to be as thin as Princess Diana.
The 57-year-old royal - who has daughters Princess Beatrice and Princess Eugenie with her ex-husband Prince Andrew - has revealed she always desired to be as "beautiful and thin" as her then sister-in-law.
The Duchess confessed: "To wish you could have a mental illness to that level is a very serious place to get to."
The royal has opened up about her struggles in a podcast with Dr Vijay Murthy, who practises holistic medicine and naturopathy.
The Duchess said she hopes to serve as a "human bridge" for people with eating disorders, encouraging them to seek out the help they need to tackle their issues.
Recalling her own experiences, the Duchess said: "The key is that I used to be a comfort eater. I used to eat to put a band aid over my emotions and I squashed my feelings through food.
"I realised that actually it wasn't a treat and in fact what I was doing was almost going to kill myself with the toxicity build-up within myself.
"I was a binge-eater. I never could get bulimia because I just didn't have that mental state to go that far, but I always wished I could.
"But that just shows you how dangerous and what place I got to. To wish you could have a mental illness to that level is a very serious place to get to."
Despite her ambition of being thinner, the Duchess revealed she never actually made herself sick.
She explained: "My body and mind was in that place, but I couldn't actually act out to make myself sick. I then grew and grew and grew."