The couple share two daughters, Princess Beatrice, 30, and Princess Eugenie, 28.
The pair legally divorced in 1996 but have remained close friends, both living together at the Royal Lodge in Windsor.
Taking to Instagram, Fergie posted a snap from Airbnb HQ in San Francisco.
She captioned the image: “Thank you for having me @joegebs and @airbnb #sanfrancisco #technology #california #airbnb.”
Fans were quick to plead with Sarah to visit their hometown in the USA.
One wrote “Sarah come to Florida” while another said “You need to come to Texas!!!”
“Will you be coming to the East coast this trip?” another social media follower asked.
Fergie's trip to the US comes after fans pleaded with the duchess to remarry her ex husband.
Attending an entrepreneurial event, the former couple inspired hopes of a continued romance.
She revealed to her many followers that she was supporting her ex husband at the Pitch at Palace Global 3.0 final.
One fan wrote: “I love how you and Andrew always support each other! You are such a beautiful family!!"
“Sarah get your handsome man and remarry!”
Another said: “Congratulations to the Duke of York for his amazing work, and kudos to you for always standing by his side and supporting him!
“You're such a great example of family! The best demonstration that sometimes reality can overcome fairytale.”
A version of this article first appeared on New Idea.