Vivian Liberto met Johnny Cash in 1951, when she was 17 and he was 19
The pair were married from 1954-66: she died in 2005, aged 71
She was born to a Sicilian-origin father and a mother of German-Irish descent
Only now has it emerged that she was black, via her great-great grandmother
Sarah Shields was born a slave to a white father and a black mother
She was granted her freedom and her 'whiteness', which passed to her children
In 1965 Liberto was pictured looking like a black woman, enraging his fans
White supremacists organized a boycott of his music; he sued for libel
Cash's team provided evidence of her 'whiteness' in the multimillion dollar suit