Of the four lord souls that were inherited by Gwyn's confidants, only 1 of those four ended not down a dark hole. Seath was the one who was given special treatment, being granted Dukedom and a giant library to pursue his research. We also see that Crossbreed Priscilla is one of Gwyn's daughters that he utterly despised even existing. It's clear. Gwyn, Lord of Cinder fucked Seath the Scaleless, and abandoned the lovechild in the Painted World to hide his tryst with his smooth and powerful lover.

look it’s been clearly stated that anyone in possession of a lord soul was ineffable, which means you can’t fuck them. it’s incredibly obvious, just go down the list

-  seath’s lower body is crystallized and gwyn was clearly not into the shy bookwyrm type anyway

- the four kings were stuck in a big shitty hole because they got tricked by a snake oil salesserpent

- the witch of izalith’s bed will sweep you into a pit

- you can’t bone nito because I mean like just look at him