The Duke of York today shared a personal photo of his ex-wife in what appears to be her home in Windsor, Royal Lodge, when she turns 59.
Prince Andrew wrote in his personal Twitter account: "Happy birthday to @SarahtheDuchess, I wish you a happy day!
The Duchess of York later shared the same image on her Instagram account, thanking Emanuel Ungaro and Jad Ghandour for their attire.
They were also behind her long emerald green dress to the floor she was wearing at the reception of Princess Eugenie's night after her royal wedding on Friday.
The couple has provoked speculation that they could be back together after appearing up close in the run up to the actual wedding of their daughter, Princess Eugenia, on Friday.
Eugenie, 28, describes them as "the best divorced couple I know", with the couple who live together in the royal residence, and who remain close for the sake of their children.
Sarah and Andrew separated in 1992 and divorced in 1996, at which time Prince Philip had included Fergie on the blacklist for having been photographed when a man had sucked her toe in Saint Tropez.
Since then, he has worked in the background trying to enchant his way back to the real signature.
The Queen has always thought that she liked Sarah, but Prince Philip can not bear to be in the same room as her, that is.
She could be seen walking away from Fergie in the official portrait of Eugenie's royal wedding, although the couple seemed cordial during the ceremony.
Sarah sat next to the Royal Family during Eugenia's ceremony, despite not being a member anymore.
She had been forced to sit back in the same church during Prince Harry's wedding with Meghan Markle.
Sarah and Andrew were seen on a family outing on horseback with Princess Beatrice a week before Princess Eugenia's wedding, putting a united front before the big day.
And they organized a joint evening reception party for Princess Eugenia and her husband Jack Brooksbank on the grounds of Royal Lodge after the champagne reception of the queen.
Real observers have speculated that the couple could be together again after years of loyalty to each other.
In case they decide to remarry, they will not be asked to obtain a permission from the Queen, after Prince Andrew went down to the seventh place of the throne, after the birth of Prince William and the third son of Prince Louis of Kate.
Only the members of the royal family up to the sixth in the throne line are obliged to ask permission from the queen.
Sarah Ferguson and Prince Andrew have gone to rescue each other in times of turmoil, and Prince Andrew paid Fergie's 1.5 million pound debts when he had financial difficulties.
In addition to sharing a house in Windsor, where Fergie has her own wing, they spend time together at their jointly owned ski home in Verbier, Switzerland.
The 13 million pound chalet, which has seven rooms, was bought four years ago with its two names.