And we summarize the lineage of Omar Bin Al Khattab as follows:
Nufayl + Sahak = Al Khattab
Al Khattab + Sahak = Hantamah
Al Khattab + Hantamah = Omar
We see that Hantamah is the mother and sister of Omar Bin Al Khattab i.e. she is the wife and the daughter of Al Khattab.
And Al Khattab is his father because he is Sahak's lover (i.e. who committed fornication with her) and her son at the same time. I.e. he is Omar's father and grandfather at the same time.
Sahak is his grandmother, mother of his father and the mistress of his father at the same time.
Al Salabah Fe Ma'rifat Al Sahabah (3/212)
Ilzam Al Nawasib. By : Nurullah Zarihi.