“Happy birthday to @SarahTheDuchess,” Queen Elizabeth‘s second son, 58, wrote on Monday alongside a photo of 59-year-old Ferguson — who is also referred to by the nickname Fergie — smiling while wearing a blue dress.
“Wishing you a very happy day!” he added.
“Their Royal Highnesses The Duke and Duchess of Sussex are very pleased to announce that The Duchess of Sussex is expecting a baby in the Spring of 2019,” Kensington Palace said in a statement on Monday.
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During the ceremony, the proud papa walked down the aisle with his 28-year-old daughter at St. George’s Chapel — the same venue where Eugenie’s cousin Harry wed Meghan in May.
“It’s a very small role, I just have to walk slowly!” the Duke of York said in an interview ahead of the nuptials, adding that he was sure his daughter would make “an absolutely outstanding bride.”
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Andrew and the Fergie wed on July 23, 1986, before welcoming their daughters Princess Beatrice on Aug. 8, 1988, and Eugenie on March 23, 1990.
Despite their growing family, there was trouble for the couple, and they announced their separation in March 1992, before officially divorcing four years later.
Since splitting, the pair has remained friendly, and Fergie actually lives at Andrew’s royal residence, Royal Lodge, in Windsor.
“I’m in and out all the time, and he’s in and out all the time,” she explained in a 2016 interview for an Australian radio show. “And no, we’re not married. We’re very happy with the way things are.”
The Duchess of York continued, “I think the great thing is we absolutely are the most extraordinary example of a unified family.”
And Fergie isn’t the only member of her family that feels this way! Eugenie has famously said, according to the BBC, “They are the best divorced couple I know.”
In fact, Fergie told PEOPLE in a 2011 article that she and Andrew get along so well that she’s asked her daughters, “Do you think Mummy and Papa should get back together again? And they say, ‘You’re great the way you are now; it’s fine.’ “