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