[5] Flodoard, writing his annals during the count's lifetime, called him Karolo Constantino Ludovici orbi filii (Charles Constantine, son of Louis the Blind), and this added byname also appears in the writings of 10th-century historian Richerus, who used Flodoard as a source.
[7] A surviving letter by Patriarch Nicholas I Mystikos testifies that Emperor Leo VI the Wise of Byzantium, father of Constantine VII, had betrothed his daughter to a Frank prince, a cousin of Bertha (of Tuscany), to whom came later a great misfortune.
That unfortunate prince could only be Louis III, whose mother Ermengard of Italy was a first cousin of Bertha, and who was blinded on 21 July 905, while the prospective bride would have been Emperor Leo's only surviving daughter at that time, Anna of Constantinople, born to his second wife Zoe Zaoutzaina.
[8] However, it is still questioned whether the planned marriage ever took place,[9] and there are chronological difficulties (not insurmountable in the opinion of Previté-Orton) in making Anna the mother of Charles Constantine.
[7] Richerus suggested that the ancestry of Charles Constantine was tainted by illegitimacy back to five generations,[7] although the meaning of this is disputed.