Niel ua Ímair

Cawley quotes Simeon of Durham but notes that "Niel" would be an unusual name in a Norse family, one theory that might explain this would be a claim made by some that a brother of Ivar married a daughter of Niall Glundubh. If Niel was a son of this couple the name would not be surprising in a Norse family and Sitric (whose parentage is also unknown) could also be a child of this couple, making him a full brother of Niel.

http://fmg.ac/Projects/MedLands/IRELAND.htm#_Toc389126206

4. [NIEL (-killed in battle 914). Simeon of Durham records that "King Niel was slain by his brother Sihtric" in 914[1242]. This reference is puzzling. It may refer to the death of Niall Glundubh King of Ireland, which is dated to 919 in Irish sources[1243]. However, no relationship with Sihtric is identified. “Niel” would seem to be an Irish rather than a Norse name.]