In the combox, Sean Brooks rightly reminds us that Harald Fairhair was an older contemporary of Gunnhild. What I also neglected to mention because I did not remember it was that Harald was Gunnhild's father-in-law. Such details are difficult to retain despite several rereadings of the relevant texts. It follows that Brigit was the grandmother-in-law of Eirik Blood-ax who was a great-uncle of Harald Hardrada. Thus, The Demon Of Scattery, Mother Of Kings and The Last Viking have slightly stronger links than I had suggested.
Sean argues against making too much of such links but they interest some readers more than others. I like to connect everything, as this blog shows. In the past, people have validated their own societies with claimed lineages and descent from the gods. Mythologically, the present Queen of England is in direct lines of descent both from Solomon of Israel and from Priam of Troy - and this expresses the fact that Western civilization combines Biblical and Classical traditions.
Reconstructed lineages make for good historical fiction. Matthew's Gospel traces fourteen generations from Abraham to David, fourteen from David to the Exile and fourteen from then to the Messiah, treating Joseph as Jesus' father. Thus, Jesus is of Jewish descent from Abraham and of royal descent from David and therefore can be the Messiah. Luke's Gospel gives a different account of the names of Joseph's father, grandfather etc and goes back through David and Abraham to Adam and God. Thus, Jesus is of human descent from Adam. John's Gospel just starts with God and the Word. Virgil has Caesar's soul waiting in the underworld to be born.