So, I close this question

Actually there were facts proven that Kovu was ment to be Scar's son. But because of him falling for Kiara it was going to end up being Incest so they changed it to him being adopted by Scar or atleast thats what disney wants you to believe.

Kovu was originally going to be Scar's real son but Disney had to change it so little kids didn't think it was ok to marry their cousins!

Sandstorm -- Not everyone sees Kovu as Scar's adopted son... Despite Disney's changing Kovu from originally being Scar's son to not in the end, it's hard to determine the actual truth. Everyone has their own theories. No one is right and no one is wrong. It is what it is.

Kovu is not scars son he was hand chosen by scar to be king

And what Disney didn't want, fanfiction can want. Ha, ha!

Kovu is'nt scar's son. he was only chosen by scar to be king once scar dies

Oh OK. Thank you for your answers!

Kovu is not the son of Scar,it is Kovu himself,and his brother Nuka that state the fact,and Seth2208 is correct,Disney did not want Kiara,and Kovu to be blood relatives.

-Celtic Lilly

Kovu is not the son of Scar. Scar adopted him, but Kovu does have blood of Zira, in which he is not related to Scar. To summarize: Kovu is not related to Simba or Kiara.
Hope this helps!