How was Fridlevus II related to Halfdan?
Fridlevus II Fridleif (Ynglinga saga) was a son of Fróði of the Skjöldung (Scylding) lineage. In that work he was the brother of Halfdan and the father of Áli the Strong.
Halfdan (floruit 782–807) Halfdan ("floruit" 782–807) was a leading person among the Danes and the first known Scandinavian to enter Frankish service. Onomastics links him to the Danish royal family since the name "Halfdan" was commonly employed both historically (as attested by the "Annales Fuldenses" under the year 873) and in the legendary royal lineage.