"Today marks the 200th Anniversary of the birth of Queen Victoria (1819-1901). She reigned for almost 64 years and I'm very proud to be named after her," Eugenie said in her post.
"The first image is a portrait of Queen Victoria by Franz Xaver Winterhalter (1805-1873) @royalcollectiontrust The second is of Emily Blunt and Rupert Friend, who played Victoria and Albert in The Young Victoria (2009) - a film produced by @sarahferguson15"
Fans were quick to express their surprise at the royal revelation, with one writing in the comments section: "I had no idea your wonderful mother produced this film. It's one of my very favourites, she's very gifted."
Another wrote: "Oh I didn't know your mum produced it, very well done!"
Eugenie's sister Beatrice even made an appearance in the film, playing a lady in waiting.
As well as producing the movie, Sarah also conceived the idea for the film.
She had been interested in Queen Victoria since her marriage to Prince Andrew, and had written two books on the topic with the help of an historian.