Many annoying comments from fans who believe Kopa is Fluffy which isn't true.

Here are 10 different comments from them from Youtube:

1. "that can't be Kiara, in these movies the males are yellow and the females are beige-colored, and that baby is yellow."

2. "that's there first child Kopa....he is a boy and Kiara's older brother."

3. "ok at the end it is not Kiara it is Kopa before the making of the lion king 2 they changed it 2 Kiara instead of being it Kopa =3."

4. "I am not a fan of lion king, but still kopa is true!"

5. "the cub is not Kiara. It's supposed to be Simba's and Nala's son, Kopi. The reason he wasn't in the second because he died as a cub. Sad I know. Look up on the story of Kopi. You'll learn more. Sorry to be a downer."

6. "OMG KOPA" XD (pointing out at Fluffy)

7. "2:18 Here comes Simba and Nala's cub, Kopa. That cub is not really Kiara (I'm not wrong). Kiara is really born on Lion King 2: Simba's Pride."

8. "Kopa, actually. Or that's the most "official" name we have for him (comes from a series of books published the same year the film was released). He got cut from the sequel (where his name would have been Chaka). That's why the majority of fans use him to fill the plot holes in Simba's Pride. The only thing we're clear on is that "Fluffy" there is clearly NOT Kiara. He has ear rims, he's younger, he's presented later in the day, and he's male, indicated by his belly fur."

9. "That cub at the end isn't Kiara, that is a male cub named Kopa. Kiara is born in Lion King 2. Look at the ears of this cub at the end. He has more golden color, has a bit hair, dark stribs around his ears and a more red color nose. If you look at Kiara in Lion King 2, she is more light. She does is more light, but does not have dark stribs around her ears and she has a darker nose."

10. "Kopa is the baby cub they show at the end.....he is the first born child of Simba and Nala but the people at Disney didn't use him in the second Lion King, but they used Kiara, Kopa's young sister......he is in the books and if u just search on youtube, "Kopa's Story" it will give a pretty good explanation of what happened to him."

But there's also fans who know that Fluffy is Kiara.
Which considers that they been ignoring the books and comics. :)

Well, the Kopa believers can't hold their breath, since TLK filmmakers ignore the books and Disney doesn't want Kopa or any of TLK:SNA non-canon characters be part of the film. Known these books are from the outsider illustrators and the creators of these books never worked with the Disney Co. Alex Simmons who created Kopa and the books he exist in says that Kopa is his creation all the way.

Disney has made it clear that Kiara is Fluffy and no one else.

Kiara's original design makes her look male by her pelt color and black rings on her ears.
But that doesn't make Fluffy (Kiara) being male just because of it's markings and colors.
Kiara looks somewhat like her grandmother, Sarabi by her ears and her pelt color can be created for females as well as known reality lions of both genders are the same colors and being golden yellow, a lioness can be created the same.
Chances of all, Mufasa can be taken after his mother and Scar taken after his father, since TLK:SNA books aren't canon. Mufasa's mother could possibly have a golden yellow pelt color like him. So, that can't make Fluffy being a boy by the pelt color. By Fluffy's belly fur doesn't show were it ends since it's chin is covering it.

But now that Simba is having a second-born cub, a male named Kion in a new film/show called "The Lion Guard which will be aired on Disney Jr in 2015. Kion will be an official TLK character unlike Kopa which is just a profit fiction character in just a few books that are release only in USA and no were else with Disney's stamp placed on them.

Here are some of the quotes and many other official stuff about Fluffy that is true:

"You think it's a king but it's a queen" by one of TLK 2 creators on a magazine.
link

"Here's Fluffy, Simba's and Nala's little cub. Let's just end it on Fluffy" One of the filmmakers of TLK on the 1995 commentary laser disc.
link

"Rafiki welcomes her to the circle of life." one of the golden books of TLK.

Fluffy's appearance in the TLK 2 trailer for baby Kiara.

Quotes from TLK 2:

Timon: "Ah, Pumbaa, look at that little guy. a chip off the old block. and you gotta know who's going to raise him."

Pumbaa: "His parents?"

Timon: "Okay sure, get technical. but who's going to teach him the really important stuff? like how to belch (burps) and dig for grubs? I'm telling ya buddy.. it's gonna be like old times. You, me and the little guy."

Rafiki: (chuckles) "It is a girl."

Timon: "Girl."

Timon & Pumbaa: "GIRL! Oy!"

Nala: "She's just like you when you were young."

Simba: "Exactly, do you realize the danger we put ourselves into?"

Nala: "You mean the danger, you put us through."

Kiara is well much like her father being mischievous like Simba as a cub.

Kiara will grow up to become a royal queen she will find her king and take her place as queen.