Sarah Ferguson on Overcoming 'Major Mental Health Problems' from Tabloid 'Trauma'

When Sarah "Fergie" Ferguson burst onto the world stage in 1985 at age 26, it didn't take long for the tabloids to descend.

In particular, headlines surrounding the Duchess of York's weight soon consumed front pages across the U.K., with others often pitting her against her good friend, Princess Diana. She subsequently struggled with anxiety in part because of relentless public bullying that included the tabloid nickname "Duchess of Pork."

"I had major mental health problems because of the trauma," says the Duchess, whose debut novel, Her Heart for a Compass, is due August 3. "It's taken a great deal of work because I believed every word that the front pages told me. It was self-shame. I'm stratospherically sensitive."

The Duchess, 61, recalls at one point going to speak to her young daughters, Princess Eugenie, now 31, and Princess Beatrice, now 32.

Watch the full episode of People Cover Story: Sarah Ferguson on PeopleTV.com or on the PeopleTV app.

"I'll never forget walking in one day to see my girls, and I said, 'I'm so sorry, girlies, because I really think I've destroyed myself,'" she tells PEOPLE exclusively in this week's cover story. "That is really dark. I had to work hard on the self-sabotage to explain it."

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Meanwhile, Diana — who was married to Prince Charles while the Duchess was married to Charles' younger brother, Prince Andrew — was often held up as the more glamorous "wife of Windsor."

"In the '80s, it was Diana looking beautiful, and there was fat, frumpy Fergie," she says of the many ways the two women were pitted against each other. "We were just there for people to make a lot of money. At the time we both didn't realize that."

The twosome who had grown up as childhood friends, would compare notes — and offer each other support.

For the full exclusive interview with Sarah Ferguson, Duchess of York, pick up this week's issue of PEOPLE, on newsstands Friday

"Diana and I both had our own mental health issues, and she and I used to talk," recalls the Duchess. "She said, 'Fergie, remember one thing: When you're at the top of the pedestal, it's so easy to fall off. And you're at the bottom. You just climb up.' We were positioned as saint and sinner. And the most important thing was to remain robust together, and we did, no matter what anyone wrote."

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