It likly the reader will never see Kiliigans mom for a long time. Potential Spoilers.
I assume that Killigan is half Bovilian and half Demon.
1) Basicly his Father is his real biological dad and his mom is either a demon or infertile bolivian and used a demon instead.
2) Alternetivly Killiggan real father is a demon and his mom only uses Killigan "Father" as a model to create her child.