Everything so far is great!
There is one thing I'd like to point out though (obviously spoilers), it's certainly not a story-breaking plot hole, and I wouldn't even be surprised if it's intentional, but I still feel like I should mention it:
The MC has some evidence that could arguably suggest that if he isn't innocent the prince would likely be involved too, it's far from definitive proof, but it's definitely there:
most motivations someone might have for killing a king would also apply to killing the rest of the line of succession
when he was outside after ball incident the MC would've had a good opportunity to approach the prince in a situation where there would likely be no witnesses, he could escape if there were witnesses or the attack went wrong, and he wouldn't be particularly suspicious if he was caught approaching the prince as long as he wasn't visibly armed, and while no one witness can confirm this, the prince could confirm his own presence, Lyall could confirm that the MC was there, and the MC knowing the prince was there (and what he was doing) would confirm that this was at the same time