Hollywood actor Tom Cruise and Arsenal manager Mikel Arteta were among the guests at the white-tie bash at Raffles London, but Prince William was also supported by family members at the event.
Amelia looked stunning in a black shimmery gown with semi-sheer sleeves from Self-Portrait, while Eliza opted for a bridal-esque white dress with a sparkly mesh neckline, also by the same label.
The sisters also accessorised their looks with diamond jewellery from De Beers. Lady Eliza sported De Beers Snow Dance Bracelet as well as the jewellers' Aura earrings and Aella ring. Meanwhile, Lady Amelia wore De Beers DB Classic Eternity Band and Aura Three Cushion-Cut earrings.
Lady Amelia married her long-term love Greg Mallett in South Africa in 2023, wearing a custom lace bridal gown by Atelier Versace. Meanwhile, Lady Eliza is dating entrepreneur Channing Millerd.
The twins are the daughters of the Earl and his first wife, British fashion model Victoria Aitken. The former couple are also parents to Lady Kitty Spencer and Louis Spencer, Viscount Althorp.
Charles has two children with his second wife Caroline Freud - the Honorable Edmund Spencer and Lady Lara Spencer.
Charles and Caroline separated in 2007 and later divorced. He is currently married to his third wife, Karen Gordon, with whom he shares a daughter, Lady Charlotte Diana Spencer.
Prince William and Prince Harry have remained close to their late mother's siblings, who also include Lady Sarah McCorquodale and Lady Jane Fellowes.
The Prince of Wales spoke about the King's cancer diagnosis for the first time at the fundraising gala as he expressed his gratitude to the public for their "kind messages of support".
During his speech, he also recognised those who wished the Princess of Wales well, as she recovers from planned abdominal surgery.
He told guests: "I'd like to take this opportunity to say thank you, also, for the kind messages of support for Catherine and for my father, especially in recent days. It means a great deal to us all.
"It’s fair to say the past few weeks have had a rather medical focus, so I thought I’d come to an air ambulance function to get away from it all."
William had temporarily stepped back from royal duties during Kate's 13-day stay in hospital in order to care for his wife and their three children.