I've come up with a mystery second cousin here on Ancestry.com. He and I share 238 cM, the largest segment being 53. We see no matches in our paper trees. I've located DNA matches for each of my four grandparents. He doesn't match any of them. I'm beginning to wonder if this isn't an example of Identical by State matches that aren't real family matches. I've read up on the topic a bit and I'm not sure that such a large common cM would indicate this situation. Does anyone know? We've checked our DNA's at Gedmatch so we know where we match but we can't come up with any other matches that we both match too. Any thoughts?