That could actually be a pretty interesting What If-scenario... Suppose Simba hadn't interrupted Kovu when he asked to talk to Kiara... I wonder what Kiara's reaction would've been when told the truth. Because I don't actually think that Kovu ever told her in the film - she just refused to believe Simba when he claimed that Kovu was part of the ambush, which by then he wasn't. But she was never told that Kovu was actually originally sent to the pride to kill her father...
Lotsa brainstorming coming up here now

If Kovu had taken Kiara for this talk it would really have been a test of where her loyalties lie. If Simba found out that Kovu was sent to be his assassin, he would most likely have exiled Kovu anyway, even if Kovu claimed to have changed. Simba had probably been looking for any reason to get rid of him anyway. Kiara would likely figure that out, and I wonder if she would hide the story from her father and in that case for how long...
The way I see it, there are several outcomes, but most would just lead back to the film's normal ending (exile, battle, Kiara + Kovu stop the battle etc etc...).
If Kiara doesn't say anything when she and Kovu come back and Simba takes Kovu on the walk to the burnt area where they are ambushed, the story could carry on "as normal" from there. But maybe with a more doubting Kiara as she goes to find Kovu? Maybe she'll search for him to find out if what her father said was true rather than "just to find him and bring him back because of the terrible injustice dealt upon him"? Maybe she would be more guilt-ridden as well, since she
knew of Zira's plan but had chosen not to tell her father?
If Simba is told the truth before he and Kovu go for their walk, we could skip the whole ambush scene and go straight to the exile. Probably without the chanting animals, but otherwise everything after that would be exactly the same.
Another outcome could be that Simba
doesn't exile Kovu and instead, to test his loyalties, asks where Zira and company are hiding and ambushes
them instead. He
could see how much Kiara liked Kovu in the scene where he lets him sleep in the cave after all, so maybe he wouldn't be so quick to banish him...
Or Simba could ask to talk to Kovu, at Pride Rock, to get as much information out of him as possible, then tell him about Scar. Because without their walk, Kovu isn't told the true story of Scar... So instead of instant action Simba would try to understand his enemies and plan things from there.
Then they could go to battle and things could play out similarly to in the film and yada yada... I think this is the theory I like the most, but it wouldn't make for very interesting screen time, since long conversation without action rarely is xP
Anyway, I'm rambling. Well done if you read all the way here
