Little is known about Himiltrude's origins. Paulus Diaconus calls her a "noble girl". The appearance of her name in the fraternity books of Alemannian monasteries may suggest an affiliation with the Germanic Alemannian or Alsatian nobility, while other sources make her the daughter of a Burgundian count and a granddaughter of Grimbert I, Count of Paris. It is not possible, however, to extrapolate any political ramifications from Charlemagne's relationship with Himiltrude.
Himiltrude probably entered into a relationship with Charlemagne during the lifetime of his father, Pepin the Younger. When Charlemagne acceded to the throne in 768, Himiltrude remained unnamed in official sources – contrary to the example set by Charlemagne's mother, Bertrada of Laon. Himiltrude bore Charles a daughter called Amaudru, who would later marry a Count of Paris; and at the end of 769 a son called Pépin. Shortly after Pepin's birth, an alliance was formulated between Charlemagne and the King of the Lombards, Desiderius. To seal the alliance, it was agreed that Charlemagne should marry Desiderius' daughter (called Desiderata by modern scholars).
Himiltrude was dismissed at that time and disappears from historical records. A grave excavated in the monastery of Nivelles was found to contain the corpse of a forty-year old woman, possibly identifiable with Himiltrude. If so, Himiltrude would appear to have died long after 770, although if and when she retired to Nivelles cannot be deduced.
Her son Pépin, who suffered from a spinal deformity and was called "the Hunchback", was eclipsed by Charlemagne's sons from the later marriage of this to Hildegard. Following an attempted rebellion against his father, he was confined to a monastery.
Marital status 
The nature of Himiltrude's relationship to Charlemagne is a matter of dispute. Charlemagne's biographer Einhard calls her a "concubine" and Paulus Diaconus speaks of Pippin's birth "before legal marriage", whereas a letter by Pope Stephen III refers to Charlemagne and his brother Carloman as being already married (to Himiltrude and Gerberga), and advises them not to dismiss their wives.
Historians have interpreted the information in different ways. Some, such as Pierre Riché, follow Einhard in describing Himiltrude as a concubine. Others, Dieter Hägemann for example, consider Himiltrude a wife in the full sense. Still others subscribe to the idea that the relationship between the two was "something more than concubinage, less than marriage" and describe it as a Friedelehe, a supposed form of marriage unrecognized by the Church and easily dissolvable. This form of relationship is often seen in a conflict between Christian marriage and more flexible Germanic concepts.
- Silvia Konecny, Die Frauen des karolingischen Königshauses. Die politische Bedeutung der Ehe und die Stellung der Frau in der fränkischen Herrscherfamilie vom 7. bis zum 10. Jahrhundert., p. 65.
- Dieter Hägermann, Karl der Große. Herrscher des Abendlands, Ullstein 2003, p. 82f.
- Gerd Treffer, Die französischen Königinnen. Von Bertrada bis Marie Antoinette (8.-18. Jahrhundert), p. 30.
- Einhard, Vita Karoli Magni, ch. 20
- Pierre Riché, The Carolingians, p.86.