Nelson Mandela's daughters insisted the royal premiere of their father's biopic Mandela: Long Walk To Freedom should continue after learning the human rights icon had died.

Prince William and his wife the Duchess of Cambridge were watching the movie with stars Idris Elba and Naomie Harris and members of Mandela's family in London in early December (13) when news of Mandela's passing broke.

Harris, who plays Mandela's former wife Winnie in the film, recalls, "We're watching the movie and half way through I get a tap and someone says, 'Come outside'.

"Idris and I and the producers, we all go outside and then we're told Mandela has died... We didn't know what to do. We thought we should stop it (movie), but they (Mandela's daughters) said, 'No, continue'."

However, the premiere's afterparty was cancelled because, according to Harris, everyone was too sad to enjoy a celebration of any kind.

She recalls, "Idris was in tears and everyone just felt really devastated. It kind of took the wind out of our sails.

"Even though we expected it and we knew he was ill, it was still a massive shock... Mandela always said that he wanted to live to 100 and he achieved so much that he set his mind to, so I always imagined that he was gonna live to 100 and from the reports that we got he was in good spirits and good health.

"I expected him to see the movie."