Since Leon Vanderkindere's seminal publications at the beginning of the twentieth century, scholars have tended to ignore the medieval report of Otto and accept Vanderkindere's proposal that Giselbert's father was Rudolf, the son of Count Nevelung.
[1] More recently, proposals have been made that Otto might have existed and been a son or nephew of Rudolf.
[3] The only record of Otto, the third continuation of the chronicle or Gesta of the abbey of St Truiden tells of the installation of Baldrick II as Prince-Bishop of Liege, and that he was the brother of Count Giselbert of Loon, and the son of Count Otto of Loon and Liutgard of Namur.
[4] Criticism of this source, written long after the facts, centres around the more detailed information it gives about Liutgard.
In summary, although there is a high chance of this being wrong, the Gestorum Abbatem Trudonensium Continuatio Tertia tells us that Otto married Lutgarde, who was from Namur, and had two sons.