Sources

1) Source: The Henry Project . External Link
https://fasg.org/projects/henryproject/data/charl001.htm. Reference: Charles "le Chauve" (the Bald) (Karolus Calvus, Karl "der Kahle") (Questionable reliability of evidence)
2) Source: Genealogia comitum Flandrensium ex libro Florido et Chronico Aldenburgensi, etc "Balduinus auter ferreum genuit Balduinum calvum ex Judith vidua Adelbaldi regis Anglorum, filia videlicet Karoli calvi regis francorum" (Data from secondary evidence)
3) Source: Genealogia comitum Bulonensium A short genealogy connecting the early Merovingians to the later counts of Boulogne, written circa the 11th century. The earliest generations are almost certainly fictional. Considered a reliable secondary source for generations from Arnulf of Metz onwards. Considered a "primary" source for events from the year 1000 onwards.. External Link
https://www.dmgh.de/mgh_ss_9/index.htm#page/300/ (Data from secondary evidence)
4) Source: Carolingian Chronicles: Royal Frankish Annals and Nithard's Histories "823... in the meantime Queen Irmengardis, their mother, died, and a short time later Emperor Louis married Judith, who gave birth to Charles.". Reference: Nithard's Histories (Data from secondary evidence)
5) Source: The Henry Project . External Link
https://fasg.org/projects/henryproject/data/ermen103.htm. Reference: Ermentrude
6) Source: Carolingian Chronicles: Royal Frankish Annals and Nithard's Histories "Oct 840... When Pepin, son of Bernard, king of the Lombards, and others saw this treachery...". Reference: Nithard's Histories
7) Source: The Henry Project . External Link
https://fasg.org/projects/henryproject/data/judit002.htm. Reference: Judith (Questionable reliability of evidence)
8) Source: The Henry Project . External Link
https://fasg.org/projects/henryproject/data/louis001.htm. Reference: Louis II le Bègue (the Stammerer) (Questionable reliability of evidence)