As the royals, cast and Nelson Mandela's daughter, Zindzi Mandela, watched the film, news broke that Mandela, 95, had died.
Zindzi Mandela and the Duke and Duchess of Cambridge, were informed of the news during the screening.
Idris Elba, who plays Mandela in the biopic, took to the stage after the film had ended to hold a moment's silcence with the film's producer, Harvey Weinstein.
'What an honour it was to step into the shoes of Nelson Mandela and portray a man who defied odds, broke down barriers, and championed human rights before the eyes of the world. My thoughts and prayers are with his family,' Idris said in a statement.
As Kate and William left the screening, the Duke told press: 'It was extremely sad and tragic news.'
Kate, dressed in a long-sleeved, floor-length cream Roland Mouret gown (which she had previously worn to a dinner at Claridges in 2012), stood by her husband as he spoke of Mandela. 'We were just reminded of what an extraordinary and inspiring man Nelson Mandela was and my thoughts and prayers are with him and his family right now,' William said.
By Olivia Marks