Hummm, im not stupid. The mirage that the Crown prince sees is definitely Elena and not Leyla. If you compare the mirage hair shape, Elena is the one that matches the mirage more than Leyla. And you cant forget that Leyla hair and eye color is paler compared to Elena. 
~ Pfp from Debut or Die
~ Character : Park Moondae
~ Character : Park Moondae
Im a normie, but when it comes to idol manhwas, I stan TT TT