Two silver-haired white women in Georgia are the distant cousins of Michelle Obama, an African American whose decedents were black slaves. 

A new book reveals that the First Lady's great-great grandfather was born to a slave on a small Georgia plantation and her master's white son.

The tale of Mrs Obama's long-lost relatives, which neither family ever talked about, shows that racial identity is even more complicated than most Americans realize. 

Joan Tribble, 69, was found to be one of those distant cousins. Her ancestor, Henry Wells Shields, owned Mrs Obama's great-great-great grandmother, Melvinia. 

Charles Marion Shields, Henry's son, fathered a child with Melvinia in 1860, Dolphus T Shields, according to DNA tests. 

Dolphus, Mrs Obama's great-great grandfather on her mother's side, was long rumored to be half-white. He had light skin and Irish-looking features. 

However, the family never talked about who his father was. It was previously unknown that he was the son of a slave owner and a slave.

The book also raises the possibility that Charles Shields, who was 20 at the time, raped Melvinia, who was just 15. The practice was not uncommon on southern plantations.