Imagine you're Leon and you grew up with the Prince of Camelot being always present and you got along well. Of course Arthur wasn't allowed to have friends or anything but he always looked up to Leon until he started growing older and he realized that nobody would take him seriously if he was kind and sweet so he tried to become like his father instead. Leon would be sad, not surprised but still unhappy about this development, especially when Arthur was cruel to servants or started boasting in front of other noble boys who thought everyone beneath them wasn't worth anything.
But then Uther sent Leon on a mission, he insisted you travel to the court of an allied kingdom under the guise of training with them and learning different styles of fighting while kind of acting as a spy. It was a long mission, and when you finally make it back to Camelot after a year away you head towards the throne room where you'd expect Arthur and Uther would wait for you. But as soon as you open the door a serving boy stumbles directly into you.
"Oh sorry." He mumbled with the sweetest smile. But you had no time to react because footsteps came up behind you.
"Merlin where were you?" Arthur grumbled at the boy over Leon's shoulder.
"I was here, George told me to come to the throne room but when I got here I was confused because your giant ego was not yet taking up all the space and I couldn't even believe how huge this room is without your abnormally large head in it so you have to forgive me for taking a moment to take it all in before I wanted to look for you. Have you had problems with getting dressed again? I'll write to my mother so she'll sent the rhyme that helped me to remember how to tie shoes when I was a child. No worries I'm sure you'll manage it eventually."
Leon would freeze right there, half expecting to hear Arthur pull his sword but instead the prince just sighed and said: "Shut up, Merlin."
