SPOILER ALERT!!!!
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Maetel/Mettel (The Crown Prince) was the red haired Serion referred to. When Louis went to motel with the red haired man; it was actually Maetel with red haired wig. If you pay attention on previous chapters, there was a scene where the author showed Maetel tried to pick up a wig from his wardrobe and one of em is colored red. The red one was the one he used when he met and went fwop fwop with Louis.
That is why, Louis cant recognized Maetel and keep on denying that 'it is possibly' Maetel coz of the distant r/s he used to experience with Maetel during school days and mainly because the man he remembered didn't resemble Maetel at all.
Ohh that's why I kinda forgot about that thanks for spoilingggg HAHAHHAHA.
As far as I know sabrina was the only one who has red hair rightttt????