The Duchess of Cambridge turned heads in the budget bling, which retails for £19.99 but has since sold out completely.
It wasn't the first time Kate had worn the bespoke Roland Mouret gown – the royal, who is known for recycling her outfits, debuted the elegant number at a ball in May 2012.
Earlier this year, designer Roland spoke about Kate wearing his design.
"I think it was quite fantastic that there was a split up the front," he told the Sunday Telegraph. "That picture of a woman when you catch a little of the leg, that's what you want to see. It's that notion of privacy."
Kate was attending the UK premiere of Mandela: Long Walk To Freedom with her husband Prince William.
The royal couple were greeted by rapturous applause from fans who had gathered at the venue to catch a glimpse of them on the red carpet. After watching the film, they were informed of the sad news that Nelson Mandela had passed away. The couple then released a statement paying tribute to the "extraordinary and inspiring man".
The Duke of Cambridge described the South African freedom fighter's passing as "extremely sad and tragic news" adding that their "thoughts and prayers are with him and his family."