Arriving with husband William to watch Natural History Museum Alive 3D, Kate looked stunning in a floor-length black lace number by Temperley she last wore at the War Horse premiere in 2012.
The royal couple donned black 3D glasses after greeting the producers and Sir David at the London museum, where Kate is patron, to see extinct creatures brought back to life on the big screen.
Produced by a Bafta and Emmy award-winning team, the film was shot by the 3D experts behind Hollywood sci-fi hit Gravity and includes visual effects from artists who worked on the Harry Potter and Lord Of The Rings franchises.
In the film, Sir David is seen staying behind the locked doors of the Natural History Museum in South Kensington, west London, as a host of resurrected beasts come to life.
Sir David said: "I have been coming to the Natural History Museum since I was a boy.
"It's one of the great places to come to learn about natural history. In this film we have the technology to bring back to life some of the most romantic and extraordinary extinct creatures that can be conceived; some are relatively recent animals like the dodo, others older like the dinosaurs, and some we only know through fossil evidence.
"Using our current scientific knowledge, this film brings these creatures alive allowing me to look at some of the biggest questions surrounding them."
Earlier, William and Kate paid their respects to Nelson Mandela by signing an official book of condolence in London.