Based on the memoirs of James Gregory, Goodbye Bafana tells the story of the white South African who guarded Nelson Mandela on Robben Island. But while it is a South African story, the $20m project is directed by a Dane, Bille August, and has an international flavour in terms of financing and casting.

Mandela is played by Dennis Haysbert (best known for television series 24), while English actor Joseph Fiennes takes the role of Gregory and Diane Kruger his wife.

Sales agent Celluloid Dreams pre-sold the film vigorously, closing deals with, among others, X Verleih in Germany, Sandrew Metronome in Scandinavia and Istituto Luce for Italy.

Speaking ahead of its world premiere in competition at Berlin, August admitted it had been daunting to portray on screen a figure as iconic as Mandela. "It was an enormous challenge and an enormous responsibility," the director said.

A two-time Palme d'Or winner (with the Ingmar Bergman-scripted Best Intentions and with Pelle The Conqueror), August has an eclectic mix of credits: he has made epics such as Les Miserables, as well as more intimate films such as death-row drama Return To Sender (2005).

In terms of research, he was not able to reach Mandela, and Gregory had died. However, August interviewed other prisoners and wardens: "I wanted to be as accurate as possible," he says.

What appealed to August about Gregory's story was that it was "unique and emotional without being sentimental".

Gregory is an ordinary man - a poorly educated white South African who is pro-apartheid because that was how he was brought up. When he is assigned to look after Mandela, he is very proud, but gradually, as he spends more time with his prisoner, he begins to change and "to recognise Mandela's ideas about a freer, democratic South Africa".

In the process, his world is turned upside down. Those he regarded as his enemies become his friends, and vice versa.

August was convinced that Haysbert was right to play Mandela. "He has enormous presence and dignity. We wanted someone who could portray Mandela's calm, dignity and intelligence ... to play the biggest celebrity in the world is tough."

When August and his producers were trying to finance the film, they approached one or two US studios. The response was always the same - they wanted more action and a stronger emphasis on the love story. August resisted. "It was important to stay close to reality. Of course, it's not a TV docudrama. We needed to make it work for the screen, but at the same time not to manipulate reality."

GOODBYE BAFANA

Based on the memoirs of Nelson Mandela's guard on Robben Island.

Budget: $20m.
Prod cos: Banana Films, Arsam International.
Co prods: X-Filme Creative Pool, Future Films, Fonema, Thema Films, Film Africa.
International sales: Celluloid Dreams
Key cast: Dennis Haysbert, Joseph Fiennes, Diane Kruger.