More so the "left to start his own pride". If he were busy with Lion Guard duties, I'm pretty sure the characters would mention him.

Definitely by the time Kiara is shown to be grown up at least. Kiara seems quite young in the sequel in the scenes where she's a cub, and in The Lion Guard she acts more mature, so I'm wondering if The Lion Guard is meant to take place sometime after Kiara has met Kovu and been told never to go back.

I don't think he was busy with the Lion Guard duties... I mean as the leader of the Lion Guard he has to protect the pridelands from intruders etc so wouldn't he be part of the last battle at least? I mean.. that's his job isn't it? Still can't find an answer :/

I don't think he was ever born.

It would probably explain why Simba was so protective of Kiara. Just a little weird to me we saw Kiara as an adult and no mention of Kion. Now Kiara is back to a cub she has a brother? Something had to have happened to him.

I don't think we're supposed to think like that! Kion didn't exist at that time because they created him just recently

And if we DO think about it then nothing really makes sense...

1. If he was busy was LG duties he would try to stop the whole battle in TLK2
2. If he disappeared the characters should at least mention him or look for him.
3. If he died I repeat the reason above... They should mention him and be sad even.
4. If he left to start his own pride they should also mention him I think

He wasn't existed in the film. TLG isn't canon of the film but rather a spin-off. Thank god I grew up with TLK which is so much better. Kion should of been a cub to Kovu and Kiara rather than another cub of Simba's when he already has a child in the canon films. Kion is like an identity of Kopa so the Kopa fans would stop bragging about "Fluffy" the cub in the ending of the first film when it's already confirmed as Kiara. I only watch the 2 films and stick with them rather than being confused of a new character who never existed in the film it's self.

I'm sorry, but for me, Kion never existed. Kiara is an only child.