The first snap showed proud dad Jack with his baby son August snuggled in his arms as he smiled at his wife Eugenie behind the camera.
While the adorable shot was new to royal fans, there was a subtle detail about when the photo was actually taken.
WATCH: Eugenie and Jack reveal royal baby's name
Back in March, Eugenie also shared new images of baby August to thank fans for their well wishes on her 31st birthday.
The tot was pictured wearing a personalised embroidered cardigan, made by Uncool Wool, and a star-printed hat from JoJo Maman Bebe – the same outfit he's sporting in the latest photo shared by Eugenie to celebrate Jack's birthday.
Eugenie shared a new photo of Jack with son August
The Princess also shared a further two snaps of Jack carrying August in an Artipoppe baby carrier, and another of the new dad enjoying a walk in a flower garden. She captioned the Instagram post: "You are exceptional. Happy Birthday my love."
Eugenie shared this family snap on her birthday in March
Eugenie and Jack welcomed their first child, August Philip Hawke Brooksbank, on 9 February at the Portland Hospital in London. One of the royal baby's middle names, Philip, pays tribute to his late great-grandfather, the Duke of Edinburgh, who passed away on 9 April.
Eugenie and Jack, who first began dating in 2010, were married at St George's Chapel in Windsor in October 2018. The couple are currently residing at the Duke and Duchess of Sussex's Windsor home, Frogmore Cottage, with their baby boy.
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