Pepin, called the Hunchback, was the firstborn of Charlemagne. Born from the king of the north-western Franks and future king of all the Franks and future emperor, Charlemagne, and from Imiltrude, young Franco-Alsatian aristocrat of modest rank.
According to Eginardo, relative, official biographer and adviser to Charlemagne, the marriage between Charles and Imiltrude was sanctioned in the frank form of the fredelehe, that is, following a practice in use among the Franks, according to a non-indissoluble form, and, therefore, Pippin and the sister, named Amaltrude (Amaudru), were not recognized as legitimate. The Imiltrude mother was repudiated in 770.
According to another accredited theory the Church of Rome exerted pressure on Charles, because it was scandalous that the sovereign of the West and protector of the church did not follow one of his most elementary norms, monogamy. For this reason, Pippin was disinherited and declared illegitimate, in order to "eliminate the evidence" of the polygamy of Charlemagne.
However, even if considered illegitimate, Pepin continued to live in court, even after his name, Pepin, in 780, had been passed to his half-brother, the third son, Carloman, who, in 781, became king of Italy.
It seems that between 791 and 792, some nobles Franks ordered a conspiracy that would have attacked the life of Charles and his three sons, Charles the Younger, Carloman and Ludwig (Lothair, the twin of Ludwig, was a child, in about 780 ). The conspiracy was discovered, in the course of 792, and in a meeting, in Regensburg, it was concluded that the same Pepin, had given his consent to take the place of his father, if the conspiracy had been successful. The penalty was very severe, all the conspirators were punished with capital punishment, which was carried out for all except for Pepin, who was obliged to take his vows, he was tonsured and locked up, apparently with the obligation of silence, in the monastery of Prüm located on the river of the same name, a tributary of the Moselle.