At age 14, Iseult is told she is to be the mother of the great king who will finally unite the disparate tribes into one cohesive nation. One night, the great king is conceived by deceit, his father using the magic of a wizard to disguise his features. The great king goes on to father a son who betrays and kills his father, and the great king is laid to rest under a hill, to await his nation's hour of greatest need.

That's what the history books would tell you. 

What actually happened is rather different.