Complex sentence: It remains a mystery who this Viking ancestor actually was and the argument that it is Somerled contradicts with Henry Lee's History of the Clan Donald and Gregory's conclusion that Somerled was of Irish Pictic descent.
Split into simpler sentences: It remains a mystery who this Viking ancestor actually was. The argument that Somerled had a Viking haplotype contradicts with the lineage described by Henry Lee's History of the Clan Donald and Gregory's conclusion that Somerled was of Irish Pictic descent.