ok, so i've done some research, i couldn't find any results of someone saying that Sans killed Asgore, but i found a wiki, and it does say that Sans killed EVERYONE, meaning he probably killed Asgore too, i'm guessing - Chrisツ

Description: AU: Underswap: DISTRUST - AU Owner: ??? - Sprites: Me - Edited: Me | Also Edited by Hammy | *Sans ATK 100 DEF 100 | *He doesn't trust you anymore for what you did. | Dialogue: Me