The sequel of the original TLK had several different scripts, which always were changed many times during production. Before Romeo-Juliett story there was planned the story about Chaka, Simba's son, and about life and death. Later this version was scrapped, and we got the Romeo-Juliett love story between Simba's and Scar's cubs, Shani (later Kiara) and Nunka (later Kovu), while Chaka became Shani's brother and then was completely cut from the story as well as Kovu's, Nuka's and Vitani's blood kinship with Scar. 

So here we have the main antagonist Zira, whose presense in the film gave birth to thousands of fanfics and headcanons and theories. Almost all fans believed that she loved Scar and wanted revenge for his death, and that she was Scar's beloved or friend so he chose one of her cubs as heir. But what if I say, that it's all lie? What if Zira has no relation or connection to Scar? What if she just made up this story with Scar's heir for own goals? The workprint of the sequel gave me some details, which perfectly demonstrate this version as the true one. And there's no need to ask authors themselves for answers. 

The workprint you can find here: https://archive.org/details/lion-king-2-workprint-vhs

The one good person gave proofs that all Zira's cubs are NOT Scar's cubs (as well as the workprint). So we will talk only about Zira and one specific story detail. 

According to the workprint, Zira is Scar's most loyal follower. NOT Scar's wife/daughter/sister/mate/beloved – she's just fanatical follower. But... what if Zira and her pride are NOT Scar's followers, but just pretended? All lionesses in the original film hated Scar and fought on Simba's side. Plus, as we know, in the original film Scar cruelly treated all, he devastated the kingdom and acted like a ruthless tyrant, everyone starved and suffered during his reign. Zira and her lionesses have nothing to admire Scar for. Think about it.

The entire Zira's claims are these:

1. Scar chose Kovu as his heir (i.e. Scar knew Kovu, Kovu knew Scar):

"He was hand-chosen by Scar to follow his pawprints and become king!" – Zira to Simba.

2. Kovu was born in Pridelands:

"Kovu was the last born before you banished us to Outlands!" – Zira to Simba.

In the deleted scene Zira also says this:

"That is our home! That is where we belong! And soon, my beloved Scar, we shall reclaim your kingdom!" – Zira to her cubs.

So, what's wrong with these claims? Well, everything. 

First of all, many people ignore one tiny detail in Zira's claim – that Scar chose Kovu himself "to follow his pawprints and become king". How and when could he do this?! "To follow his pawprints" – it means "To kill the previous king and conquer the kingdom and power by force". Scar could not choose anyone for this mission before the battle on the Pride Rock, because he did not suspect the existence of Simba (that Simba is alive). Scar had no idea that he will be overthrown, and he only feasted with the hyenas; during the battle he would not have had time to do this – he tried to hide and escape during battle and then was chased by Simba and later fought with him. Plus, he ruled alone and wasn't interested in getting a queen and making cubs. He was lonely character, who needs no one, while the hyenas were just his army.

In the workprint of the sequel Zira says this:

"Don't be a fool, Nuka! Kovu is the chosen one! We must fulfill Scar's dying wish and train Kovu to become king!" – Zira to Nuka.

What kind of dying wish, if Scar tried to run away, fought with Simba and then was eaten by the hyenas and burned in the fire?! He couldn't survive even for few seconds at all! 

Second, Kovu couldn't be born in Pridelands. He has no memories about Scar. All he says is either "Scar was not my father" or "I heard about Scar this, but what you tell now, I never heard" type of lines. 

Also in the deleted scene Zira proudly says this:

"Remember, Scar took you in and accepted you as his own son. Yes, he wasn't your father, but he chose you to become the next king." – Zira to Kovu.

You can notice that she is the only character, who insists this, while Kovu is pretty unsure and uncertain in this scene, we see how Zira brainwashes him (under false attempt to cheer him up), so her claims about accepting Kovu as son by Scar can't be the truth at all. 

So, when Kovu was born? In the workprint we find out that Kovu was born before Kiara, and he already is pretty grown up cub during Kiara's presentation. However, Rafiki discovers Kovu's existence exactly after Kiara's birth and presentation, he refers to Kovu as "What is this? Another cub? Where he can be? In the Outlands... where Simba banished Scar's followers...". I.e. Rafiki didn't know about Kovu until the day of Kiara's birth and presentation.

Plus, as the sequel demonstrates, Simba and the pride never knew that "Scar had a heir", they didn't know about Kovu, since Simba refers to Kovu just as "the cub". Plus, Zira only now introduces Kovu to Simba:

"Haven't you met my son, Kovu? He was hand-chosen by Scar to follow his pawprints and become king!" – Zira to Simba.

So, why Zira mentions this only now, but not during/before banishing? And how Simba and others didn't see any cubs (or even newborn cubs) in Zira's pride and literally were okay with their banishing? I doubt that Simba is so cruel to banish innocent little cubs to die from hunger and thirst. 

I'm genuinely sure that Kovu was born after Scar's death and after Zira's banishing. Zira just made up this story for gaining power. She didn't love Scar, he was just a manifestation of her desire to rule the Pridelands. Don't believe me? In the sequel Zira says this:

 "I now see the path to our glorious return to power!" – Zira to Kovu and her pride during My Lullaby song.

In the workprint Zira also says this: 

"[Scar is dead] because of Simba! If not for him, Scar would still be the king!" – Zira to Vitani.

Then she dreamily adds this to herself:

– "And I, Zira, his devoted queen!".

That's it. Zira is angry toward Simba not 'cause of banishing or Scar's death, but 'cause Simba returned and deprived her of the opportunity to legitimately seize power, i.e. the possible chance to become queen. She wants power, Scar for her is just the manifestation of her desire, nothing more. 

I think, it's the irrefutable evidence that Zira just lied to all about "Scar was close with me and chose my youngest son as king" thing and just wanted to get the power and used her son for this.

P.S. If you mention TLG, I can confidently say that TLG also perfectly fits to this version of events. Remember, chronologically TLG happens during youngth of Kiara. In TLG Scar returned as the vulcan spirit. And during the show he never mentions Zira, he never mentions Kovu or choosing him as his heir, as if he never knew about their existence at all. Absolutely nothing despite the fact that while Scar and his henchmens fight with Kion and his friends, at the same time Zira and her cubs and pride chill in the Outlands and don't participate in this, knowing nothing about Scar's resurrection and so on.