There have been many debates about who Nala's father is or might be.
Alot people believe either Scar or Mufasa fathered Nala. That'd be okay...If Scar and Mufasa weren't brothers and Simba(who is Mufasa's son) didn't have cubs with Nala at the end of TLK. I don't believe Scar is Nala's father. I also don't believe Mufasa fathered here either. If any of these were true i'd be incest as Nala would be Simba's cousin of Half-sibling.
So who could be Nala's father?
Maybe the male from the comic "An unusual choir."?
http://smg.photobucket.com/albums/v625/ ... hoir01.png
Only friends and family are allowed at the celebration, yet Nala has no relation to anyone in the picture (nor does she know anyone except Mufasa, Sarabi, and Simba)...or does she? The scruffy version of Mufasa could be her father...which is why her fur color is similar to one of the his newborns(who would be her half siblings if he WERE her father giving her a greater reason to go.).
Another suitor would be "King" Joe; A myserious lion Simba meets in the pridelands. Most fans are inclined to believe Scar fathered Nala and, seeing he is Simba's uncle, it would make Nala Simba's cousin and wouldn't be has bad as having the same father. Scar also let Nala live during his reign. This can be overruled as he let Chumvi and Kula live, Chumvi being a danger to his kingship. But still, it's incest all the same. Joe looks exactly like Scar, but isn't related to the royal lions in any way.