Board Thread:General Discussion/@comment-30178351-20160405091519/@comment-26242189-20160418134325

Ehem. Allow me to clear this up.

'THERE IS LITERALLY NO SOURCE IN THE GAME THAT CONFIRMS THAT GASTER WAS THE FATHER OR BOTH THE SKELEBROS COMBINED. THE ONLY SOURCE THAT WE HAVE OF THIS ARE FROM THE UNDERTALE FANDOM THEMSELFS, TUMBLR AND REDDIT. THIS IS FANNON, AND IS NOT CANNON.'

That should do it.