That has to be how he knew enough to make illusions of people they know. Dennis wasn't real either, and that's kind of a relief after the way he turned back to Academia.

But it's just one among a lot of cruel and careless actions of the Prince. He kidnapped people, hurt Reira, abused his servants, drugged them and invaded their minds and used Strange's wife against him...

Yuya's expression pulls back in distaste. "The Prince is a creep. He's the worst!" He's hardly seen someone so morally depraved since the Professor, but he really takes the cake.

And now that they don't have to abide by his rules, Yuya can insult him as much as he feels like! That freedom incenses him, and he swings a fist through the air as his grief gives into anger. "I'm going to make him regret this!"