The Duchess of York paid a glowing tribute to Andrew, whom she married for a decade and insisted "my duty is for him".
Sarah – also known as Fergie – described her royal wedding to 1986 as the "happiest day" in her life in an interview with Daily Mail.
Asked if the couple should marry, the duke does not rule out the possibility.
Sarah said, "So many have asked me, but we are so pleased with the way we are right now.
"We enjoy each other's business: we allow each other to flourish. I know it sounds like a saga, but it's the way we are."
Andrew and Sarah have maintained a close relationship despite their divorce in 1996, with the couple even sharing their Royal Lodge residence in Windsor.
The couple sat on a united front at her youngest daughter Princess Eugenie's wedding to Jack Brooksbank last month.
Sarah described her relationship with Andrew as "our story."
The duchess said, "We are completely compatible. Our words 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 for him. I'm so proud of him. I stand at him and always want. How we are is our story.
"Although we are not any, we really believe each other. The York's is a united family. We have shown it. You saw it at the wedding."
The Duke's latest comments about Andrew come after the couple previously described themselves as "the happiest unmarried couple in the world".
Sara and Andrew were separated in 1992, months before the infamous photo appeared by the duchess with the toes kissed and sucked by John Bryan during a vacation in France.
The embarrassing picture is believed to have completed the breakdown of Sarah and Andres marriage, with the couple divorce four years later.
But Sarah was welcomed back to the royal family last month for Eugenie's Windsor wedding.
Proud Sara looked happy when she saw Eugenie marry Brooksbank in a spectacular ceremony at St George's Chapel.