People think the cub is a girl because One of the lion king creators said something like "The second movie continues where the first left us with a twist- We think that the cub is a king but turns out to be a queen!" (Not exact quote, I have not memorized it )
I don't believe in Kopa so I think it is Kiara.

-DP, Die Hard Lion King fan

Kopa exists in the book universe, but not in the movie universe. I believe it is Kiara at the end of the Lion king. Kopa is not existant in the lion king official movie storyline, but he is in the books. You can believe in Kopa if you like, but I do not really believe he exists. Sorry Kopa fans. Don't take it personal.

It is most likely that Disney did not plan at first to make a sequel. So they created a random cub that looks like a male.

But after deciding to make a sequel and writing in for kiara to be a girl, they couldn't change what fluffy looked like.

So, that's pretty much it.

BluetheWolfDog: actually, Fluffy isn't neccessarily an early version. Many people (myself included) think it is Kopa, but Kopa wasn't invented at that point, nor was a sequel planned (or expected, as they didn't think it would be popular enough) ruling out Kiara, so it was just a cub, but since The-Cub-At-The-End-Of-The-Movie is a long title for it, they named it Fluffy.

well fluffy is an older version of kopa so i dont think fluffy should be offical since its just kopa but yeah people have different opions but I'd say likley boy since its just kopa in a different version

Because they have their own free willed opinion.

iv allways seen him as a male cause in a book i had as a kid it said "his son"

True.... Thanks Aiyana-Kopa

Well what Seth said is very correct. But I think it really should be that they think its male, becuase regardless of a name or history of whatever, basically every TLK book, bar a few made after TLK2 (even some made after TLK2) say that the cub is a boy/a prince/the new lion KING. Wouldn't people think it was male?

Another reason is that some people may think Kopa or Tanabi are real in the TLK universe, but they think of Fluffy as ANOTHER cub, and males aren't generally called Fluffy so they make it female.

Thanks Seth2208