"So proud of @hrhthedukeofyork on parade today for The Colonel’s Review with @grenadier.guards at Horseguards and also my girls," Sarah commented on the post.
She also shared close ups of Andrew alone and on horseback.
In another post she shared a snap which shows the Duke of York standing next to Her Majesty, Queen Elizabeth II on Buckingham Palace’s balcony alongside other royals.
Andrew is riding his horse in the second, while Eugenie and Beatrice stun in the third picture as they wave from their carriage.
Sarah captioned the photos: “Happy Birthday Your Majesty and very proud of Andrew, Beatrice and Eugenie at Trooping the Colour today.”
Fergie's fans couldn't contain their excitement at the possible meaning behind the posts.
One commented: “Can’t wait for the news that you’re remarrying, a proper fairytale ending.”
Another said: “Andrew and the girls looked amazing only you should of been there too, hopefully soon. Much love to my favourite Royal Family.”
Trooping the Colour celebrates the Queen’s official birthday.
Her Majesty’s actual birthday was on April 21 when she turned 93.