Edward Cunningham Harrison … was John C. Allen Sr.’s biological father.
A recap: my great-grandfather’s mother, Mary Brown, married Graham Allen in 1876 in Charles City County, Virginia, during her pregnancy. Except that he was a white man, we knew nothing of John’s birth father’s identity, and I didn’t really expect ever to.
However, a few months ago, I got an estimated 3rd cousin DNA match at Ancestry DNA. I was intrigued. I have only six matches at that level. Three are with known paternal cousins, and all are African-American. Except this one. A.B. is all Great Britain and Ireland and Scandinavia and Europe West.
I sent A.B. a message, and then a follow-up. She responded, and we briefly explored a dead-end or two. I examined A.B.’s family tree more closely. Two of her great-grandfathers were from Richmond, Virginia, which is just up the road from a couple of the counties in which my maternal grandfather’s forebears lived. One of A.B.’s great-grandfathers was Edward C. Harrison; the other, John S. Ellett. I inquired about both men, and she told me that her Harrisons had lived in Charles City County. We were getting warm. I asked A.B. to upload her raw data to Gedmatch, where I quickly determined that she is a solid second cousin match to my mother and maternal uncle. I told her that I believed that we were related through my great-grandfather and that Edward C. Harrison was the right age and in the right place at the right time to have been his father. A.B. immediately asked what she could do to help figure out the connection. I asked if she would test with 23andme, and she readily agreed. So did her sister.
A couple of weeks ago, their results posted. My mother, my uncle, my sister and all six of my first cousins have tested with 23andme. All of us match A.B. and her sister M.H. The closeness of the DNA matches confirm a recent common ancestor, and all signs pointed toward Harrison. I needed to eliminate Ellett though.

A.B. and my mother, 267 cM total match.
In reviewing my matches, I noticed that T.N., a long-time and fairly close match, also listed Harrison among his surnames.

From my mother’s 23andme matches — sisters M.H and A.B., T.N.’s mother, and T.N.
I also found that T.N. matches A.B. and her sister and, most importantly, they all share matching segments of the same chromosomes with my Allens. This “triangulation” proves that all of us descend from a common ancestor.

Partial screenshot of comparisons of chromosome matches of T.N. to my mother, A.B., M.H., and my uncle. (That Chromosome 7 segment gave me life. It’s the stuff of dreams.)
I sent T.N. a message and mentioned that, based on chromosome share, I thought that our common ancestor was William Mortimer Harrison, father of Edward C. Harrison. T.N. responded, forwarding an old email from his uncle that detailed his family’s history. T.N., in fact, is descended from Edward C. Harrison’s sister Caroline and thus from William M. Harrison, as I’d guessed. He is a third cousin to A.B. and to my mother, and he has no Ellett ancestry. Thus, Edward C. Harrison is confirmed as A.B. and my mother’s direct ancestor. (T.N. is descended from a separate Harrison line through Caroline’s husband James P. Harrison, her distant cousin. Relative chromosome shares between A.B. and my line, however, eliminate James as our common ancestor.)
Through Edward, we are descended from or related to the oldest colonial families of Virginia — Harrisons, Randolphs, and Carters, among others. A signer of the Declaration of Independence. Two presidents. Pocahontas. (Yes.) These families were also owners of several of the large plantation houses still standing in Charles City County, including Westover and Berkeley. (At this time, however, I don’t think that any of my forebears were enslaved in the area.) I’m not sure how John Allen’s mother Mary Brown met Edward C. Harrison or what the nature of their relationship was. She was from Amelia County, and there was a Harrison branch there, but I don’t know if she knew them.
A.B. is ecstatic to learn that her grandfather had a half-brother. So is her sister M. My family, too, is amazed. I’m hoping that, with their help and some deep sleuthing, I will learn more about the circumstances of John Allen’s birth. And I may meet A.B. when she comes to Georgia next month.
The truth will out. DNA tells the tale.