In the aftermath of King Arthur's demise and with Queen Guinevere in hiding, a new prophecy emerges:

Powers that were, powers that be, there's only one who holds the key. Sword of dark and sword of light, only one can make it right. Born of sin and kind of heart, a power hidden from the start. From out of two there comes one, a child of a forgotten son. A power to find, a power to duel, a power to ignite and the last to rule.

Between light and darkness, only one can rule.