Princess Beatrice was joined by friends and family for a masked ball at Windsor Castle ahead of her 18th birthday.
Princess Beatrice will be 18 next month
The theme of the evening was 1888 with guests wearing a variety of period costumes.
The princess, her sister Princess Eugenie, 16, and their parents the Duke and Duchess of York joined in the event wearing outfits from the Victorian era.
The date was chosen because Beatrice, who is fifth in line to the Throne, was born at 8.18pm on 8/8/1988.
Princess Beatrice was wearing a blue and gold gown by British couture label Marchesa for her 18th birthday party.
Her mother and sister were wearing outfits by Barbara Matera Ltd, the New York-based theatrical costume designers.
Georgina Chapman and Keren Craig, of Marchesa, said Princess Beatrice had had a clear idea of what she was looking for in her costume.
"We worked closely with her, incorporating elaborate details in order to produce a finished silhouette that was truly unique."
Royals the Earl and Countess of Wessex, Peter and Zara Phillips as well as veteran broadcaster Sir David Frost were among the guests expected to attend.
Around half the 500 guests were invited for dinner with the rest joining later for champagne and canapés.
Musicians, performers and three members of the Circo Rum Ba Ba circus troupe provided the entertainmnent.
In her first interview last year the princess told society magazine Tatler she did not see herself as a "stereotypical princess".