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).
A grave excavated in the monastery of Nivelles was found to contain the corpse of a forty-year-old woman, possibly identifiable with Himiltrude.
Charlemagne's biographer Einhard calls her a "concubine"[4] and Paulus Diaconus speaks of Pepin's birth "before legal marriage".
[1] A letter by Pope Stephen III seemingly referring to Charlemagne and his brother Carloman as being already married (to Himiltrude and Gerberga), and advising them not to dismiss their wives, has led many historians to believe that Himiltrude and Charlemagne were legally married.
The acts of Adalard of Corbie supports this hypothesis, for his monastic vocation is described as due to the scruple he had regarding Charlemagne's dismissal of Princess Desiderata of the Lombards which occurred before any consummation of the marriage and possibly before any religious ceremony (it is unclear whether the marriage ever took place or if Desiderata only received the homage of the nobility in accordance with her planned future position of Queen of the Franks).