Eugenie posted two photos to her Instagram Story on Thursday, showing Beatrice admiring her vintage gown when she visited Windsor Castle ahead of the dress going on public display on Wednesday.
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Sharing one snap of Beatrice gazing at her dress, Eugenie wrote: "Beatrice viewed her beautiful wedding dress yesterday, which went on display at Windsor Castle today.
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Another image showed Beatrice standing beside the dress as it sits in a large glass display box, with Eugenie adding a funny Gif of Ariel from The Little Mermaid blowing a kiss over the photo while donning her own wedding frock.
Captioning the photo, Eugenie jokily wrote: "You can see it (sadly not Bea she has left by now) at Windsor Castle if you are visiting the castle."
Beatrice viewed her dress ahead of it going on display to the public
The exhibition, which opened to visitors on Thursday, also features Beatrice's wedding shoes and a replica of her bridal bouquet.
The dress was loaned to Beatrice by her grandmother, the Queen, who first wore the gown for a State dinner in Rome in 1961. Her Majesty also wore the dress again to the London premiere of the film Lawrence of Arabia in 1962 and the State Opening of Parliament in 1966.
The Queen wearing the dress in 1962
The gown is made of ivory peau de soie taffeta, and the skirt is trimmed with a band of ivory duchesse satin. It also features geometric hand embroidery in crystals and diamantés over the bodice, waist and hips.
Sir Norman Hartnell’s original design was altered for Princess Beatrice under the direction of Angela Kelly, personal advisor, dresser and curator to the Queen, and the British fashion designer Stewart Parvin.
Beatrice and Edoardo married at the Royal Chapel of All Saints in Windsor
The Royal Collection Trust says: "The full-skirted silhouette was softened to give a more contemporary, simplified shape, and the underskirt and petticoats were recreated and bound with silk tulle.
"Short sleeves of triple organza were added to the straps and embroidered with vintage diamantés to match the original Hartnell embroidery design. Each alteration made to the dress is reversible."
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