While Beatrice plumped for a floral dress from designer of the moment The Vampire’s Wife, Eugenie wore a chic, nude dress by French label Sandro.
And of course, both ladies chose to wear their signature head pieces for the occasion.
As for the Queen, the monarch looked delightful in head-to-toe baby pink – even matching her umbrella to her outfit.
Keen to share the occasion with her fans, Princess Eugenie shared some special snaps from the event via Instagram.
"This afternoon, my sister and I attended a Garden Party at Buckingham Palace in support of Her Majesty,” she wrote.
"I really enjoyed meeting such a diverse group of people who were all invited in recognition of their work in their respective communities."