Gertrude's grandfather killed Baldur

According to Book III of the Gesta Danorum (Deeds of Danes) of Saxo Grammaticus (Saxon Grammar-man), Rorik Ringslinger was the son of Hodur, he who killed Baldur with the mistletoe. Boe, another of Odin's sons, slew Hodur. So the Swedes, the Curonians and the Slavs rebelled against Denmark. When Rorik Ringslinger organized his shrunken kingdom, he appointed Horwendil to govern Jutland. Horwendil won so much fame pillaging that Rorik let him marry his daughter, called Gerutha or Gertrude. They had a son, Amleth. But Horwendil's brother Feng grew so envious that he slew his brother in order to marry Gerutha and rule Jutland. Knowing that his uncle was guilty and his life was unsafe, Amleth feigned madness...