Board Thread:Fun and Games/@comment-33186754-20180523213026/@comment-35806478-20190403050912

“In the playable epilogue to the True Pacifist Route, the Dogi appear outside Snowdin library with the other Snowdin dogs and Endogeny. The amalgamate is revealed to contain the parents of both of the Dogi, and they muse on whether this means they are now married to their sibling before dismissing it as something dogs often do regardless.”

See? Siblings.