Chronicon Lethrense and Annales Lundenses
The Chronicon Lethrense (and the included Annales Lundenses) tells that Haldan (Healfdene) had two sons, Helghe and Ro (Hroðgar). When Haldan died of old age, Helghe and Ro divided the kingdom so that Ro ruled the land, and Helghe the sea. One day, Helghe arrived in Halland/Lolland and slept with Thore, the daughter of one of Ro's farmers. This resulted in a daughter named Yrse. Much later, he met Yrse, and without knowing that she was his daughter, he made her pregnant with Hrólfr Kraki (Hroðulf). Helghe later warred in Wendland and killed the king of the Wends. He also won all of Denmark by killing a Hodbrod. Lastly, he found out that Yrse, with whom he had slept, was his own daughter, went east and killed himself.
Both Helghe and Ro being dead, the Swedish king Hakon/Athisl (i.e. Eadgils) forced the Danes to accept a dog as king. The dog king was succeeded by Hrolf Kraki.
Read more about this topic: Halga