Pendragon Legacy Series by Katherine Roberts

It is the darkest hour of the darkest Age. King Arthur is dead, killed by his wicked nephew, Mordred. Saxon invaders rampage across the land and forces of evil are gathering. The path to the throne lies open to Arthur's only remaining flesh and blood - Mordred. But there is one with a better claim than Mordred - Arthur's secret child... moreIt is the darkest hour of the darkest Age. King Arthur is dead, killed by his wicked nephew, Mordred. Saxon invaders rampage across the land and forces of evil are gathering. The path to the throne lies open to Arthur's only remaining flesh and blood - Mordred. But there is one with a better claim than Mordred - Arthur's secret child. Brought by Merlin to enchanted Avalon as a baby and raised there for protection, the king's heir must take up a vital quest: to search for the four magical Lights with the power to restore Arthur's soul to his body. Introducing Rhianna Pendragon: unlikely princess and Camelot's last hope. less

Rhianna Pendragon faces her toughest quest yet...King Athur's soul lingers in Avalon's enchanted halls, while his daughter, Rhianna, seeks the four magical Lights that can bring him back to life. She must venture deep into Dragonland to find the Crown of Dreams, the third light, which contains all the secrets of her ancestors. But Mordred knows that any Pendragon who wears the crown can claim the throne and he wants both for himself...