Sarah, Duchess of York feared she had been handed a "death sentence" when she was diagnosed with breast cancer.
The 64-year-old royal - who was married to Prince Andrew from 1986 until 1996 and has daughters Princess Beatrice, 36, and Princess Eugenie, 34, with her - underwent a single mastectomy after being diagnosed with the disease last June and explained that her mind went to the "darkest places" when she initially received the news.
Writing for The Sun newspaper, she said: "When you’re told you have cancer, you can’t help thinking it’s a death sentence.
"Your mind goes to the darkest places and you wonder what lies ahead and how you are going to share the news with your family.
"That was certainly the case for me last year when a routine mammogram detected breast cancer, something I had always dreaded.
"I had almost missed the appointment as I couldn’t face a journey into central London on a hot summer’s day and thought I would put it off."
The Duchess almost missed the appointment in the first place because she couldn't face the trip to the clinic, ad revealed that the "life-saving" moment only came about at the behest of her sister Jane.
She added: "I’m living proof of the importance of never skipping screening appointments and always getting symptoms checked out promptly."
Fergie was also found to have skin cancer earlier this year, and while she has been warned against using the term "cancer-free", she has found hope in fact that the "treatment has been successful and tests show there has been no spread or recurrence" since diagnosis.
She added: "I’m reconciled to the fact that I will have to have checks for the rest of my life.
"I’m now determined to do whatever I can to raise awareness by sharing my experience."