Taking to Instagram, Sarah shared a gorgeous video montage of her stunning garden with daffodils among the flower beds and text scrolling over the top, which read: "Happy Birthday dearest Eugenie. When I see the colour of spring, I think of your birth and what a gift you are. Budding with colour and love xx."
WATCH: Sarah Ferguson's sweet birthday tribute for Princess Eugenie
Fans loved the post and took to the comments section to wish Eugenie a happy birthday.
Sarah also shared two childhood photos of Eugenie, one of which showed the royal mother and daughter riding on a carousel and another of Eugenie sitting amongst some flowers, wearing a sweet pink bonnet.
The Duchess wrote in the caption: "The joy of children. In deep gratitude for my luck in my glorious girls. Happy Birthday Eugenie..."
Sarah also shared childhood photos of Eugenie
The couple will no doubt celebrate Eugenie's first birthday as a mum at home in private with their baby boy. The family are based at Frogmore Cottage, Prince Harry and Meghan's UK residence, which is also a stone's throw away from Eugenie's parents' home. Sarah and her ex-husband Prince Andrew are good friends and still live together at Royal Lodge in Windsor, despite their divorce in 1996.
After the arrival of their first grandchild, proud grandmother Sarah told HELLO!: "I am so excited and thrilled to have become a grandmother. August Philip Hawke Brooksbank, a wonderful grandson and he brings such joy, smiles and love to all our family."
She continued: "Jack and Eugenie are and will be superbly caring and wonderful parents."
Eugenie is celebrating her 31st birthday
Eugenie is tenth-in-line to the British throne after her older sister Princess Beatrice; her newborn son August is therefore eleventh.
The Princess has been sharing a handful of photos of her baby boy on Instagram. She proudly announced his arrival on 9 February with a close-up snap of her and Jack holding their son's tiny hand. Eugenie captioned the sweet picture with three blue heart emojis.
Eleven days later, she announced his name, writing on Instagram: "We wanted to introduce you to August Philip Hawke Brooksbank. Thank you for so many wonderful messages. Our hearts are full of love for this little human, words can't express.
"We are excited to be able to share these photos with you. By our wonderful midwife. Thank you to the wonderful essential workers including our midwife who came to discharge our boy."
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