She had smiled and posed for photographs on the red carpet and then enjoyed an animated conversation with the Duchess of Cambridge.
And if Zindzi Mandela had any idea that their father's long life was drawing to a close, she did not betray it for a minute.
Then, in a single instance, everything changed. As she was about to watch the London premiere of his incredible story, she and sister Zenani were apparently told that the 95-year-old had died peacefully at home after months of illness.
Tearful and flustered, Zindzi tried to compose herself. But asked if she wanted the film - Mandela: Long Walk To Freedom - to continue, she said yes.
It was an extraordinary premiere. Few in the Odeon auditorium in Leicester Square knew what had happened and settled down to enjoy an evening celebrating one of the most iconic figures of the 20th century. The Duke and Duchess of Cambridge were informed of his death discreetly by an aide shortly before the end of the movie.
It was only after the credits had rolled that the film's producer Anant Singh got on the stage to break the news to the rest of the audience. There were screams and gasps of shock while some burst into tears. A two minutes' silence was held.
Eleanor Simmonds, 54, from Croydon, who was at the premiere to support a Mandela charity, said: 'There was an audible sharp intake of breath.
It was shocking news to hear at the end of the film. Everyone was shocked,' she said. 'I was really, really sad news because it was a wonderful evening.'
William and Kate looked ashen-faced as they walked down the stairs into the foyer. Speaking as he left the Odeon cinema, the Duke said: 'I just wanted to say it's extremely sad and tragic news. We were just reminded what an extraordinary and inspiring man Nelson Mandela was.
'My thoughts and prayers are with him and his family. It's very sad.'
Shortly after the Royal couple left, shocked members of the audience began emerging from the cinema, in silence at first.
The cast, whose after-show party was promptly cancelled, were too upset to speak. In the foyer, security men surrounded Naomie Harris, who plays his wife, Winnie, as she walked slowly past, head down and close to tears.
In a statement Idris Elba, who is tipped for an Oscar for his portrayal of the great man, said in a statement: '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.'
John Battersby, 65, a South African journalist who knew Mandela personally and wrote the afterword to his authorised biography said: "My daughter told me just before the announcement. Apparently he died half an hour before the film started.
'My phone was buzzing in my pocket but I just thought 'who is calling me in the Mandela premiere? In the protection of the darkness I shed a few tears.
'He was brilliantly portrayed in the film, what came through was the dignity.'
His daughter Anna said: 'I think it's very fitting that we were all here paying tribute to him at the moment of his passing.'
It was not clear what had happened to Mandela's daughter, Zindzi but she did not leave with the rest of the audience.
Earlier in the evening she had appeared jovial and relaxed as she walked the red carpet.
Speaking before the showing, she said: My father is fine. He's 95 years old and he is pretty frail. We are hoping to see more of him.
'(The film) is something that makes me feel really proud, what my family went through and the role my father played has been recognised. It is a reward [for him].
'When we document our history in this manner we do it not just for ourselves but also for the future generations, young people that my father is really passionate about.
'He has seen clips of the film and said he saw [Idris] that he thought it was him.'
She added: 'When my 11 year-old grandson saw the movie last week I asked him what did he thought and he said 'the dude who played grandad when he talks he kind of reminds me of him'.
'I said: 'What about the lady who play big mammy? [Winnie Mandela]. He said: 'That chick, I think she's hot!'
Starring British actor Idris Elba, 'Mandela' follows the iconic anti-apartheid leader’s extraordinary life from childhood through to his 27-year imprisonment on Robben Island and, finally, his inauguration as the first democratically elected President of South Africa in 1994.
The film itself, which has been 16 years in the making, has received mixed reviews from critics, but Elba, who is best known for his role as a detective chief inspector in the hit TV series Luther, has been praised as ‘towering’ and ‘Oscar-worthy’.
Speaking on the red carpet last night he told Mail Online: 'Everyone knows who Mandela is, everyone has an idea of what he sounds and looks like. I worked really hard to pull in all the elements, from the sound of his voice to the way he walks.
'I don't look anything like him but it was really important the audience got a sense of who Mandela is because the likelihood is that we will never meet him in person.
'For somone who doesn't look like Mandela you have got to work harder to get the audience in there.
'I think he [Mandela] has seen parts of the film but ultimately it's about his life, he's been there, he's done it - so he might not even need to see it.
'Tonight is extra special because this is my country and when the royals come out to watch a film it's. a big deal. I feel very proud that it's my film, really proud.'
On Wednesday his daughter, Makaziwe Mandela, insisted he was ‘still with us, strong, courageous’ but admitted for the first time that he was on his 'deathbed’.
'Even for a lack of a better word... on his deathbed he is teaching us lessons - lessons in patience, in love, lessons of tolerance,’ she added.
'Every moment I get with him I'm amazed.
'There are times where I have to pinch myself that I come from this man who is a fighter even though you can see he is struggling, but the fighting spirit is still there with him.'
Each year the Royal Film Performance is staged to raise funds for the Cinema and Television Benevolent Fund, which supports industry employees and their families in times of hardship.
Also benefitting from this year’s event is The Nelson Mandela Children’s Fund, which works with the disadvantaged youth of South Africa.