"sometimes I like to imagine how Hollow Knight would have looked like if he was allowed to grow just like his sibling that is currently holding the infection.

Since by the Abyss it is shown that they have all round like heads with the exception of horns, and the only grown Knight we see has that curved moon like shape head, I like to imagine they most likely grow to similar shapes unless the horns are on the sides of the head. So since Hollow’s very similar to his sibling, I tried to keep that same similar too. The big difference is that its head is much rounder and the horns have a shorter points separation and it keeps the 2 points."