Princess Eugenie shared a sweet tribute to her sister, Princess Beatrice to mark her birthday yesterday (8 August).

Taking to her official Instagram account, Princess Eugenie shared a some sweet photos of the princesses on the beach together, cosied up in hats and scarves.

"Happy birthday to my big sissy.. love you so much xx" Princess Eugenie wrote alongside the snaps.

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The pair's mum also took to instagram to post some sweet throwback pics with Princess Beatrice in honour of the special day.

Sarah Ferguson posted two sweet photographs of the two of them, including one of Princess Beatrice as a little girl in the back of an open top car, wearing pink sunglasses.

"Happy birthday Beatrice. You’ll always be my girl. <3" Sarah wrote to her daughter.

Last year, Princess Eugenie shared similar posts in celebration of her sister's big day. In a caption, she wrote, “Happy Birthday to my special big sissy,” adding, “Love you so much,” and finishing the message with cake, balloon and celebration emojis.

In the first image, Princess Eugenie and Princess Beatrice stand cheek to cheek, smiling at the camera in co-ordinating cream outfits.

In the second, they pose with cousin Zara Tindall for a sunny selfie in vibrant summer dresses.

Another image shows the pair arm in arm at the National Service of Thanksgiving, which took place at St Paul’s Cathedral, London, in June earlier this year to celebrate the Queen’s Platinum Jubilee.

Princess Beatrice wore monochrome blue with a bow-topped hat while Princess Eugenie opted for a vibrant orange dress and a black, asymmetric hat.

In a final image, the pair pose next to a poster for Floodlight from the Anti-Slavery Collective, which was co-founded by Princess Eugenie and looks to be a project her sister is supporting her efforts in.

Princess Beatrice's husband, Edoardo Mapelli Mozzi also shared a sweet tribute to "the world's best wife."

He added, "Along with this, you are the best mother in the world. We love you so very much. Happy birthday my darling," with a photograph of the Princess smiling on the banks of a river.