Film director Amma Asante came across an old photograph taken in Nazi Germany of a black schoolgirl by chance.
Standing among her white classmates, who stare straight into the camera, she enigmatically glances to the side.
Curiosity about the photograph – who the girl was and what she was doing in Germany – set the award-winning film-maker off on a path that led to Where Hands Touch, a new movie starring Amandla Stenberg and George MacKay.
It is an imagined account of a mixed-race teenager’s clandestine relationship with a Hitler Youth member, but it is based on historical record.
Warning: Some people may find some of the content of this article upsetting
In the Nazi era, from 1933 to 1945, African-Germans numbered in their thousands.
There was no uniform experience, but over time, they were banned from having relationships with white people, excluded from education and types of employment, and some were sterilised, while others were taken to concentration camps.
‘Disbelief and dismissiveness’
But their story has largely been untold – and it has taken Ms Asante 12 years to get her account of the period on to the big screen.
“Often there’s a form of disbelief, of questioning, sometimes even a dismissiveness of the difficult lives these people led,” she told the BBC about the reaction she received from some when she spoke about her research for the film.
The African-German community has its origins in the country’s short-lived empire. Sailors, servants, students and entertainers from present-day Cameroon, Togo, Tanzania, Rwanda, Burundi and Namibia came to Germany.
Once World War One broke out in 1914 this transient population became more settled, according to historian Robbie Aitken. And some African soldiers who fought for Germany in the war also settled there.
But there was a second group whose presence went on to feed into the Nazis’ fear of racial mixing.
As part of the treaty that was signed after Germany’s defeat in World War One, French troops occupied the Rhineland area of western Germany.
France used at least 20,000 soldiers from its African empire, mainly North and West Africa, to police the area, some of whom went on to have relationships with German women.
The derogatory term “Rhineland bastards” was coined in the 1920s to refer to the 600-800 mixed-race children who were the result of those relationships.
The term spoke to some people’s imagined fears of an impure race. Made-up stories and racist caricatures of sexually predatory African soldiers were circulated at the time, fuelling concern.
While anti-Semitism occupied a pre-eminent place at the heart of Nazi ideology, a line in Mein Kampf, the book published in 1925 outlining the political beliefs of party leader Adolf Hitler, linked Jewish and black people.
“It was and is the Jews who bring the Negroes into the Rhineland,” Hitler wrote, “always with the same secret thought and clear aim of ruining the hated white race by the necessarily resulting bastardisation.”
Once in power, the Nazis’ obsession with Jews and racial purity gradually led to the Holocaust, the industrialised slaughter of six million Jewish people during World War Two, as well as the mass murder of Roma, people with disabilities and some of the Slavic peoples.
Mr Aitken, who researches the lives of black Germans, says they were targeted too – albeit not in the same systematic way.
He describes them as being assimilated into the Nazis’ “spiralling radicalisation of racial policy”.
He says evidence shows their policies toward “other ‘racial aliens’ hint toward a goal of racial annihilationism”.
‘I felt only half-human’
In 1935, the Nuremberg laws, which among other things outlawed marriages between Jews and other Germans, were passed. These were then amended to include black people and Roma in the same category as Jews.
But a fear of racial mixing persisted and in 1937 the mixed-race children from the Rhineland were targeted for forced sterilisation.
Hans Hauck was one of at least 385 people who underwent the operation. Mr Hauck, the son of an Algerian soldier and a white German, appeared in the 1997 documentary Hitler’s Forgotten Victims.
He spoke about how he was taken in secret to have a vasectomy. He was then given a sterilisation certificate, to allow him to carry on working, and he had to sign an agreement saying he would not marry or have sex with people “with German blood”.
“It was depressing and oppressive,” he told the documentary makers, “I felt only half-human”.
Another victim, Thomas Holzhauser, said on the film: “Sometimes I’m glad I couldn’t have children. At least they were spared the shame I lived with.”
Very few others spoke about their experiences while they were alive, and “there have not been many attempts to uncover what eventually happened to the majority of them”, Mr Aitken, who is one of the few historians working on the subject, told the BBC.
“It is worthwhile remembering that the Nazis also wilfully destroyed many of the documents pertaining to camps and to sterilisation, making it difficult to reconstruct the fates of groups and individuals,” he said.
Ms Asante, who has also written and directed Belle and A United Kingdom, says many of these people suffered an identity crisis. They had a German parent and saw themselves as German, but they were also isolated and never fully embraced.
“The children were inhabiting two places at the same time. They were both insiders and outsiders,” the 49-year-old said.
Though their experiences differed, all black Germans were subjected to persecution under Nazi rule.
Germany’s colonial era, especially the attempted genocide of the Herero and Nama people in Namibia, already led to a negative view of Africans.