Zuko is Ozai's son. Currently there have been zero indications that that would not be the case. In the least he's officially his son, however there is nothing that states or indicates that Ursa would have made a slip.
I see, but my friend said something about "The Search" comic that was coming out
Yes that one is going to be about the search for Zuko's mom, however there is still nothing that indicates Zuko would not be Ozai's son. The first few pages of The Search have already been released as a sneak peak and I can't find anything that supports that statement.
My friend told me this today that Fire Lord Ozai isn't Zuko's real father so is this true??
no, read my rep.Pretty sure he is his son.
Well, after reading the book, The Search, at the end, Zuko finds a note from his mom, ursa, and Ozai and Ursa were married by an arrangement but Ursa was already engaged to another man, so when Zuko finds the note, it was from Ursa to the man she was engaged to and loved and it says, how every time she looks into THEIR SONS eyes, she sees him. So, no. Zuko and Ozai are not related. Hope this helped.