Series: Pendragon Legacy 1
Source: won from Feeling Fictional
The blurb says:
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. 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.