In the first snap, Jack is seen pushing little August along in his stroller.
In the second, Eugenie and Jack smile for a selfie near the coast, with little August bundled up against his mum.
The third and fourth images capture precious moments between Jack and August as the dad holds his son close.
The last in particular stands out: It captures Jack falling asleep with his son fast asleep on his chest - sneakily snapped by Eugenie in a quiet moment.
Eugenie's fans were over the moon with the insight into the new parents' adventures with their newborn.
"Oh, these pictures are just adorable, Eugenie," one follower wrote adding: "The last one is the essence of peace - so sweet! Thanks for sharing these photographs with us, & hope Jack enjoyed a wonderful first Father's Day."
Another fan pointed out a cute comparison: "I hope this doesn't sound silly, but I can see our Queen in August."
"Happy first Father's Day to Jack, I hope he enjoyed his day and thank you Your Royal Highness for sharing these special images," a follower added.
The Cambridge family also celebrated dad-of-three Prince William, who celebrated Father's Day with his children at their country home, Anmer Hall.
In new images, the Prince was seen at the annual Sandringham half marathon with his two eldest children, Prince George, seven and Princess Charlotte, five.
The family also shared a cute graphic to Instagram featuring an unseen picture of Wills and his three kids snapped on the day of Trooping The Colour in 2019.
Prince Charles' official Instagram channel, Clarence House, also shared a heartfelt post with the father's in his life.
The first featured an old photo of Charles and his dad, Prince Philip who sadly died in April this year.
In another sweet snap, the future King is seen with his own sons Prince Harry and Prince William.
And in two other pictures, Camilla, Duchess of Cornwall's father Bruce Shand is featured - her dad passed away in 2006.
Buckingham Palace also joined the festivities on behalf of The Queen, posting a candid snap from 1951 of Elizabeth with her father, King George VI and her husband Philip and their eldest son George.
"To mark #FathersDay we are sharing this photograph of The Queen with her father, King George VI, and Prince Philip watching a young Prince Charles sitting on a statue at Balmoral," the Palace captioned the beautiful image.
This article originally appeared on our sister site, Now To Love.
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