The 54-year-old Duchess of York said she was spurred into fitness action when she reached the same weight she was when pregnant with Princess Beatrice.
"I used to be so angry. I believed I was never going to lose the weight. I was just drowning in food," she went on.
"It took courage to go out in public in all the years I have been overweight.
"Every time there was a 'Duchess of Pork' or 'Fat Fergie' headline, they didn't have any idea they were reaching to the depths of my soul."
Fergie took action and flew out to Swiss ski resort Verbier for a gruelling boot camp training regime which saw her lose three stone in five months.
Read the full interview in the latest edition of HELLO! which is out now.