Fergie and Andrew tied the knot in 1986 and divorced ten years later.
Despite being removed from The Firm after a scandal saw pictures released of the Duchess having her toes sucked by a prominent businessman.
The scandal opened a rift between Fergie and the Royal Family, with Prince Philip reportedly being unable to share the same room with her.
However, she successfully remained close to Andrew, with whom she continued sharing their marital house, the Royal Lodge, in Windsor.
Fergie added that she and Andrew are still living a "fairytale."
She said, “We both say it. We are completely compatible.
“Our bywords are communication, compromise and compassion.
“July 23 1986 was the happiest day of my life. Andrew is the best man I know.
“What he does for Britain is incredible; no one knows how hard he works for his country.
“My duty is to him. I am so proud of him. I stand by him and always will. The way we are is our fairytale.”
The Duchess also opened up for the first time about rumours she was set to remarry Andrew.
She said: “We’re so happy with the way we are right now.
“We enjoy each other’s company; we allow each other to blossom.
“I know it sounds like a fairytale but that’s the way we are.”