I've literally just done this after triggering the second phae like three times.
I've noticed late that after staying at the throne after maybe one or two deaths, the hero could literally deal no damage to me ^^'!
At first i thought the lack of sword damage was because of the above, and that the bow damage was so small that i wasn't seeing it...
But after making an accidental dash, i realized i had truly become "Undying"! LOL