However, Kate's best accessory of all was her husband, William, who suited up in a fitted tux.
The royal couple were given a warm welcome from an excited crowd as they walked the red carpet looking regal at the Royal Albert Hall in London on Sunday.
The Duchess went for an nearly bridal look, donning a sweeping, one-shoulder white gown by her favourite designer Alexander McQueen. In June 1997, Diana wore the earrings without the drop to a performance of Swan Lake at Royal Albert Hall, one of her last public appearances before her death in August. The adorable moment saw Kate whisked off by BAFTA Chief Executive Amanda Berry, quietly saying her apologies to those nearby as she climbed the steps through the audience.
The Duke of Cambridge has been the president of the British Academy of Film and Television Arts since 2010, when he took over from Sir David Attenborough.
The mum-of-three also wore Princess Diana's diamond and south sea pearl dangle earrings, with an equally exquisite diamond bracelet.
Meanwhile, at the BAFTA Awards, The Favourite dominated the list of winners while Roma took home the top two prizes - Best Film and Best Director - of the evening.
Rami Malek won the best actor award for his portrayal of the late Freddie Mercury in Bohemian Rhapsody while Mahershala Ali was awarded best supporting actor for his role as a pianist in Green Book.