Eugenie, 29, wore a graduated pastel high-neck dress embellished with iridescent flowers by Peter Pilotto, the designer of her world famous royal wedding dress.
The Queen's granddaughter teamed the summery sleeveless number with an edgy pair of silver Valentino stud stilettos and a small peachy cream handbag.
Big sister Beatrice, 30, opted for a more casual look with a simple red day dress and sparkling gold loafers.
Beatrice covered up in a fashion forward black fringe jacket and slung an emerald green bag across her body.
The famously close royal sisters looked delighted to be in each other's company.
The Princesses are said to have a deep bond with an age difference of just one year between them and the shared experience of growing up under the watchful eye of the press and public.
Watch the video below to hear Princess Eugenie describe her relationship with her big sister!
Bea's new love Edo, as he is known, looked dapper in a navy suit, white shirt and relaxed beige trainers.
Earlier in the day, Princess Eugenie joined her aunt and uncle Prince Edward and Sophie, Countess of Wessex, to deliver the Duke of Edinburgh Gold awards on behalf of her grandfather, Prince Philip.
Taking to Instagram, the royal shared her own set of pics that showed the princess mingling and joking with the award recipients.
"Honoured to join my Uncle and Aunt, The Earl and Countess of Wessex today at Buckingham Palace to hand out @dofeuk Gold Awards," wrote Eugenie.
"It was fantastic to meet all the young men and women who have achieved so much."
Eugenie's choice of loose-fitting dress continues to fuel speculation she is expecting her first child with husband Jack Brooksbank.
Watch this video for all the clues another royal baby is on the way!