The adorable image showed the Princess kneeling down to pick up her son as he hugged her tightly and appeared to have been taken at the Van Gogh exhibition in London.
Eugenie also posted a portrait of her mother, Sarah Ferguson, who is a doting mum and granny.
The royal captioned the images: "Happy Mother's Day to every mother out there." Her followers were clearly delighted by the photos, and rushed to the comment section to share their approval.
WATCH: Princess Eugenie becomes teary as she recalls introducing baby August to Prince Philip
"Aww, this so sweet," commented one, while another added: "Hope you’ve been spoilt rotten today Eugenie!!!!" A third chimed in: "Happy Mother’s Day," while others simply posted rows of heart emojis.
While the Princess has tended to keep her son, who turned one in February, out of the public eye, this is the second photo of the little boy that she's shared this week.
Princess Eugenie shared the sweet mother-son moment to Instagram
The 32-year-old made an exception for two special events, posting the earlier picture on Wednesday in honour of her own birthday.
Eugenie celebrated with a day out with her son and her husband, Jack Brooksbank. Her Instagram showed a beautiful image of the young family as they walked hand-in-hand through a park.
The snap showed the setting sun, which created the perfect backdrop as it shone through the trees.
Eugenie and Jack welcomed their son in February 2021
Eugenie rocked a gorgeous floral dress and white trainers while her husband kept things casual yet stylish in a green hooded jumper, a pair of jeans and black Converse trainers.
His striped top peeked out from underneath his jumper, which appeared to match August's striped trousers – how cute! "What a birthday to celebrate in the park with my boys. Thank you Xx," the royal mum captioned the photo.
Fans complimented the picture, writing: "Happy birthday, this is such a sweet photo" and: "Beautiful picture for your birthday. God bless you and your family."
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