Crown of a King, Book Three of The Carolingian Chronicles — J. Boyce Gleason

Despite his best efforts, the only thing to reign after Charles Martel's death is chaos. His daughter refuses to marry a Lombard prince. His two eldest sons question the rights of their younger pagan stepbrother, and the Church demands a steep price for their support. Son battles son, Christianity battles paganism, and Charles's daughter flees his court for an enemy's love. Based on a true story, the Carolingian Chronicles are a whirlwind of love, honor, sacrifice, and betrayal that follows a bereaved family's relentless quest for power and destiny.