Chadley's mother cheated on his father with a skeleton man. It took about three years to realize "How is that possible?" then the Gaster's theme song rolled in, the author's eyes blank like *Hatty Hattington voice* "WTF JUST HAPPENED?!?!?!?!??!" Then the author laughed at it, knowing it was never possible. Plus that would mean Sans and Papyrus and Chadley would be brothers. Which would be pretty fucked up so no.