William had the chance to see the flower at the Singapore Botanic Gardens - home to orchids named after a host of world figures from Nelson Mandela to Margaret Thatcher.
The event was a poignant moment for the Duke as Diana was due to visit the Far East nation to see the flower but was killed in a Paris car crash in 1997 a few weeks before the visit.
With Kate by his side, William looked thoughtful as he clasped his hands and stared at the white flowers of the orchid named Dendrobium Memoria Princess Diana.
The Duke could be heard praising the delicate blooms, saying "It's beautiful, it's beautiful" before smiling.
The visit had a lighter moment as another orchid, specially propagated, was named Vanda William and Catherine after the visiting royal couple.
With its attractive white blooms covered with purple spots, the plant stood out - as did Kate who, in keeping with the theme, wore a kimono-style pink dress decorated with an orchid pattern by designer Jenny Packham.
The Duke and Duchess of Cambridge visit Singapore