I wrote about the Melungeons of East Tennessee and Appalachia several years ago after doing some research for my Dad's cousin Hubert. He asked me to find out if his great grandmother Eleanor Marzenah Bunch was Native American.
I came across the story of the Melungeons because her family name, Bunch is associated with the group. The stories said they were descendants of either Native Americans or early Portuguese explorers. My research showed no connection between Marzenah's family and the Bunch family in East Tennessee.
Well now they have released DNA test results on dozens of people who had family ties to the Melungeons and all the tests show their ancestors came from Africa not Europe.
In fact, offspring of sub-Saharan African men and white women. There have been court cases going back 150 years where family members successfully argued they were not black but Portuguese. A necessary claim to live in peace during the slavery and post Civil War era.
DNA doesn't lie, you don't always get results that are this definitive from the tests for genealogical research but you always find out something you didn't know before.