The duchess made the confession during a radio interview with Australia's KIIS FM breakfast show. When asked who was the last person she got tongue-tied over, Sarah replied: "I always get really nervous before meeting the boss."
Princess Beatrice and Princess Eugenie's mom was referring to her former mother-in-law the Queen, but she added: "Of course, she's brilliant. She makes you feel comfortable within the first five seconds."
It wasn't long before Sarah was quizzed about her relationship with her friendly ex Prince Andrew, with whom she's remained close since their 1996 divorce. The Duchess, 57, even said the couple had "never really left each other".
"Do you think you and Andrew will get back together like the world wants Kourtney Kardashian and Scott Disick to get back together?" asked radio host Kyle Sandilands.
"I always think, 'Have we really?'" replied Sarah. "We're divorced to each other right now. We've never really left each other."
"You're still together sort of," pressed Kyle.
"Yes," she replied, before vaguely adding: "I think the happily ever after... I'm actually writing a book about that too."
Sarah and Andrew have remained exceptionally close and have always put the welfare of their daughters Eugenie and Beatrice first.
"I look at them and think 'wow,'" said Sarah. "No matter what I've done in my life, there's one thing I know 100 per cent is I've been a really good mother."
Earlier this year the duchess and Prince Andrew spent what would have been their 30th wedding anniversary – 23 July 2016 – together. The former couple spent the day at Royal Ascot, where Sarah was attending as a guest of her ex-husband.