Immediately I messaged S and grilled her about the pseudonym/real name. I told her the number of cMs I shared with that match. The only possibilities for a match of that strength are: half sibling; aunt/uncle; niece/nephew; double first cousin; or grandparent/grandchild.
This. Was. Huge.
S had corresponded with B. S had reached out to B, explaining as an adopted person she was looking for biological family. S and B communicated for a time. B provided some information. B was able to point to their MCRA (Most Common Recent Ancestor).
Because of another mutual relation to S and me, we discovered the MCRA between us.
With that information, combined with the information S received from B I was able to determine B is my aunt, my donor's sister. I figured that out around midnight, using the AncestryDNA app on my phone, in bed. I thought, 'This seems promising. I'll check my work in the morning on Ancestry.com but for now I'm going to go to sleep.' As I was closing my app to attempt to sleep I saw an obituary for B's mother. I was sad to learn B's mother was deceased. Given the relative ages it isn't surprising, nonetheless sad.
If B is my aunt, then her mother, R, is my grandmother. I had no choice but to immediately read my grandmother's obituary. This obituary is what I now call the "Golden Obituary." If you're familiar with genealogical research, you are aware of what a goldmine an obituary can provide. Often not a primary source they must be considered with some skepticism. However, the information they provide, when supported by primary sources, can be revelatory as was the case with this one.
This particular obituary listed the names of each of R's children, two daughters and one son. One son. One. Son. If she only had one son, and she is my paternal grandmother, her one and only son is my donor.
Reader, do you think I was able to ease into a gentle slumber at what was then one o'clock in the morning. I tell you now that would not have been possible.