How was Fridlevus II related to Halfdan?
Halfdan Halfdan (Old Norse: "Halfdan" , Old English: "Healfdene" , Medieval , Proto-Norse: "*Halbadaniz", "half Dane") was a late 5th and early 6th century legendary Danish king of the Scylding (Skjöldung) lineage, the son of king named Fróði in many accounts, noted mainly as the father to the two kings who succeeded him in the rule of Denmark, kings named Hroðgar and Halga in the Old English poem "Beowulf" and named Hróar and Helgi in Old Norse accounts.
John, Prince of Schleswig-Holstein Johan of Schleswig-Holstein (9 July 1583 – 28 October 1602) was the youngest son of Frederick II of Denmark and Norway and Sophia of Mecklenburg-Schwerin. He went to Russia in 1602 as the bridegroom of Boris Godunov's daughter Ksenia (Xenia), but fell ill and died before the marriage could take place.