I have recently discovered through an Ancestry DNA test + GEDMatch that my Aunt is my half-Aunt and that she and my mother don't share the same biological father. Looking at my Aunt's DNA Matches on GEDMatch she has 2 close relatives who we don't know and who aren't a DNA Match for my mother or I. Jacob who shares 503.7 cMs with my Aunt and Jacobs's full biological sister Sophia who shares 347.8 cMs with my Aunt and is also an X-Match with her with total segments: 69.2 cM (36.405 Pct). Jacob and Sophia's X-Match is Total segments = 86.1 cM (45.349 Pct)
I can narrow it down to definitely being on their father's side as they have 4 half-siblings (shared mother) who my Aunt's not a match with. Also, Their paternal grandmother's side has Irish roots which explain my Aunts 42% Irish when my mother and I are 0%. Jacob is 36% Irish.
The relationship calculator says it's most likely Half-Cousin or 1st Cousin once removed but does the X-Match mean anything? I can't add that into the calculator.
Jacob and Sophia aren't their real names.
Update: I added my Aunt's DNA to MyHeritage and it came up that she has a DNA match with 179.7 cM shared. I contacted The match and we found a common ancestor that would make them 2nd cousins once removed (Which is exactly what MyHeritage DNA predicted) if my Aunt's father is Jacob and Sophia's great uncle. If my Aunt's Father is Jacob and Sophia's half Uncle that would make my Aunt's new match and her 3rd Cousins which the DNA calculator says is only a 9.88% chance. I asked the new match to upload their DNA to GEDMatch and they only share 41.1 cM with Jacob and 46.7 cM with Sophia. so I think this new information definitely rules out my aunt being their half-cousin. The DNA Jacob and Sophia share with the new Match makes it that there’s only a 10-14% chance they're 3rd Cousins which is confusing.
Well, The MyHeritage DNA Match has given me more information on her tree. I can't see the whole thing as it's on private because she's dealing with her own ancestry drama's. The information has raised more questions then it's answered. Her G-Grandmother is called Hannah, she thinks that Hannah's parents are her and my Aunts common Ancestors. But, I don't have them having a daughter called Hannah, I have them having a daughter called Anna born the same year. Which, they could be the same person, but Hannah married Anna's first cousin... I know what people think about small country villages but this would be the first 1st Cousin relationship or anywhere near that I've ever seen while using ancestry, it definitely wasn't as common as people think.
If Hannah was Anna and the MyHeritage DNA Match was my Aunt's 2nd Cousin Once Removed AND 3rd Cousin once removed wouldn't they share more then 179.7cM?