The Lifestone Chronicles. Foundation of a King's Legend

This, the trilogy of the Lifestone Chronicles begins with:-

Foundation of a King’s legend
The story of the boy Arthur, who is destined to be the King of Kings; he unwittingly usurps a lawful and expectant boy King in waiting, which becomes a battle between good and evil, a battle between boyhood friends, with supremacy as the prize. In theory it is the battle to end all battles, whilst creating the foundation of the entity which becomes the Lifestone. The dark lord is created, the magic unleashed, the future of all hangs in the balance...