Complex sentence: The main protagonist of the series Roland Deschain is also descended from Eld thus making them distant cousins and this is the key to which Roland can defeat the King as stated in prophecy laid out during the course of the series.
Split into simpler sentences: The main protagonist of the series, Roland Deschain, is also descended from Eld, thus making them distant cousins. This is the key to which Roland can defeat the King, as stated in prophecy laid out during the course of the series.