In Norse Mythology, Jormunrek is the King of the Goths who fell in love with Gudrun's daughter, Swanhild. Even though Gudrun agreed to let them be married, Jormunrek's son Randver fell in love with Swanhild before the wedding and Jormunrek's advisor Bikki told Randver to tell Swanhild he loved her and Jormunrek that the pair were lovers. Jormunrek had the pair put to death

Gudrun had her sons Hamdir, Sorli, and Erp avenge their half-sister's death. Erp was killed by accident en route, but Hamdir and Sorli maimed and killed Jormunrek. The story can be found in more detail in this chapter of the Volsunga Saga.

Source:
http://www.timelessmyths.com/norse/norseminor.html