I'm also guessing that it was the duke but who knows perhaps it could be the prince and wa...

I'm 95% certain it's the duke bc of the hair of that blurry figure. The prince's hair is messier, and the blur had less strands sticking out, slicker hair, like the duke's.

And I hope to god he didn't SA him but used some magic or something that left bruises on his... Idk, mana vital point holes or something. But it's just wishful thinking on my part...

I hope so too