The author's nephew met a distant cousin after a cheek swab test
DNA testing has revealed Roots author Alex Haley was descended from a Scotsman.
Researchers found his nephew is distantly related to a woman from south Wales who has traced her lineage back to 17th Century Scotland.
Haley's best-selling novel told how his mother was descended from an African man kidnapped into slavery.
The DNA evidence supports anecdotes that another ancestor was a white man working on a slave plantation.
The author's nephew Chris Haley provided a cheek swab for a new DNA testing service offered by a genealogy website.
The sample revealed he was related to June Baff-Black, who had submitted a DNA sample taken from her father.
The distant cousins were introduced to one another at a Who Do You Think You Are? event in London on Saturday.
Alex Haley achieved international acclaim with his 1976 novel, Roots: The Saga of an American Family, loosely based on his family history.
Roots author suspected he had a white ancestor but lacked proof
The central character was Kunta Kinte, an ancestor traced through his maternal line, who was kidnapped in The Gambia in 1767.
In another novel, Queen, he relied on oral history to trace another family line back to a William Baugh, an overseer of an Alabama slave plantation.
Alex Haley died in 1992 without having established any independent corroboration for the account.
Olivier van Calster, managing director of website ancestry.co.uk, which carried out the research, said DNA testing was a useful new tool for family historians.
"As Alex Haley knew only too well, at its core, any family history is a combination of established facts and reasonable assumptions," he said.
"With science such as DNA becoming increasingly popular for use in furthering family history, it is exciting to see many of those reasonable assumptions - even 300-year-old ones - becoming established as facts."