Edoardo posted the sweet snap on Instagram, writing: "Happy Birthday Baby Girl. You bring us so much love and joy every day."
The image showed little Sienna, with her back to the camera, wearing a long-sleeved pink and red floral dress with a wide-brimmed straw party hat.
The picture appears to have been taken outside, with a walled garden seen in the background.
Beatrice and Edoardo have not shared any official images of Sienna since her birth in 2021, preferring to keep their daughter off their social media accounts.
Earlier this year, Beatrice's sister, Princess Eugenie, shared a sweet photo of her eldest son August with Sienna as the cousins enjoyed a play date at London Zoo.
Sienna has also not joined her parents for any formal public events. The little girl is currently tenth in line to the British throne, but is not likely to become a full-time working royal in the future.
Her mother Beatrice has a full-time role at tech company, Afiniti, while her father Edoardo has his own property development and interior design company, Banda Property.
Sienna was christened during a private ceremony at the Chapel Royal at St James's Palace in London, when she was around six months old, it was confirmed in April 2022.
The tot also has an older half-brother, Christopher Woolf, known as Wolfie.
Beatrice and Edoardo tied the knot in Windsor in an intimate ceremony in July 2020, when there were restrictions around weddings due to the COVID-19 pandemic at the time.
The princess wowed in a remodelled version of one of her late grandmother the Queen's Norman Hartnell gowns, and was loaned Queen Mary's Diamond Fringe Tiara, which Princess Elizabeth also wore on her wedding day to Prince Philip in 1947.
Listen to HELLO!'s A Right Royal Podcast and find out the surprising shoes the late Queen wore under her robes...