Abd. Guillermo de Navarra

https://fmg.ac/Projects/MedLands/NAVARRE.htm

King Teobaldo I had four illegitimate children by unknown mistresses:

10. GUILLERMO de Navarra ([1225 or after]-30 Dec before 1267). The Chronicle of Alberic de Trois-Fontaines records that "comes Campaniensis Theobaldus" had "filium nomine Guillelmum bastardum", dating the event to "quo tempore rex"[666]. As the same passage records the arrival of Thibaut in Navarre to join his uncle in 1225, it is assumed that "quo tempore rex" is intended to mean "during the time his uncle was king" rather than "while he [Thibaut] was king". The marriage dates of the illegitimate daughters of Thibaut indicate that they must have been born before his accession, which also suggests that this interpretation of the phrase in the Chronicle is correct. The Chronicle also adds in the same passage that "episcopus Pampelone" was "frater uterinus eiusdem bastardi", giving a clue to the identity of the mother of Guillermo. A priest.