I've had a theory but i don't think it's true anymore. So, she did mention the grand duke realized his feeling towards the original FL when she was sleeping, right? so, maybe the grand duke was the one that patted her when she was asleep, and then fell for her? or at least took a liking to her. Unless it was love at first sight. She also mentioned that he liked the original FL's sincerity, and she was quite sincere when she was in the bathroom, right? But, what made me think it's not true anymore, is that I looked back into the grand duke's outfit and he wasn't wearing gloves. Also, I think it's a bit too much falling for her (or even for a grand duke to pat her) like that. So, maybe it's the king at the end. Idk.