It is certainly worth noting that the issue of Gorm's ancestry is widely debated and far from resolved.  Many believe that Hardecnute Vurm is a single individual (ie, Gorm "Hard Knott") and not father and son.  An excellent reference in this regard is The Foundation for Medieval Genealogy and the page concerning DENMARK, Kings:

http://fmg.ac/Projects/MedLands/DENMARK.htm#_Toc147312862

  deBailleul