Who is "Lucius"?

If it's the usual cliche story then he's probably the prince of the other kingdom. Or the brother/step brother of the prince :)

Oh he's almost definitely the prince. Boy from a different country and a summoner just like the foreign prince not to mention the mom told him to hang out with her daughter so she must be in on it. Also the dude mentions that she'll hate him when his secret is known which sends up some real big flags. The fat and ugly part must be a rumor or something