Pope Stephen III
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.