|Nithard, as Abbot of St. Riquier|
Charlemagne was so insulted by the idea that he broke off ties to England and refused to allow English ships to land at Frankish ports. Charlemagne was very wary of the idea of allowing his daughters to marry, lest they produce potential heirs to the throne that created future problems. He had no plans to marry any of them off.
The daughters, however, were not isolated, and two of them seem to have found "arrangements" that suited them. Rotrud bore a son, Louis, to Rorigon the Count of Maine. Bertha had a relationship with Angilbert (later an abbot, and even later a saint!) that produced two sons, one of whom was Nithard.
We don't know much about Nithard's upbringing. He was well-educated, as all Carolingian children with connections to the Court would be, but whether it was at the palace school or under his father at the Abbey of St. Riquier isn't known. He was made abbot of St. Riquier like his father, and aided his cousin Charles the Bald in the conflicts that occupied the descendants of Charlemagne.
We remember Nithard now for his historical works. He wrote four books on the history of the Carolingian empire after Louis the Pious. His Historiae or De dissensionibus filiorum Ludovici pii ["History" or "On the Dissension of the Sons of Louis the Pious"] provides an excellent firsthand account of the conflicts—not always accurate or unbiased, but detailed in ways only an eyewitness to the events could produce.
So far as we can tell, he died of wounds received during a battle in June 844. When Angilbert was exhumed in the 11th century, and his body found to be uncorrupted (lending aid to the idea of his canonization), Nithard's body was found with him.