When an African prince and a white middle-class clerk from Lloyd's underwriters got married in 1948, it provoked shock in Britain and Africa.

Seretse Khama met Ruth Williams while he was a student at Oxford University. After his studies, he was supposed to go home to the British Protectorate of Bechuanaland (now Botswana) and marry someone from his own tribe, but his romance with Williams changed everything.

His family disapproved and Khama was forced to renounce his claim to the throne. The British government came under pressure to show its disapproval and Khama was exiled from his homeland.

He later became the first president of Botswana when it became an independent country.

Witness spoke to Ruth Williams's sister about the love that conquered prejudice.

Witness: The stories of our times told by the people who were there.