[Childe finds Elise and Luke fairly quickly, chatting them up for a moment before he turns back around to lead them over to Aether. But by the time he manages to do so, some other person is dancing with the prince- someone he doesn't know. As he watches, he looks to the other two and asks:]

Do either of you know who that man is?

[Luke only shakes his head, explaining that he's never seen that person, though it's hard to tell because of the mask. The man doesn't seem to get too close to Aether, well, until he does get close. He can see Aether's body tense up, and a small fire ignites inside of him. It's one thing to let Elise or even Luke, if he so chose, dance with Aether, but this guy...that's not okay. He can see how uncomfortable Aether seems to be, and he can't take watching it anymore.

Childe stomps forward, with Luke crying a small Hey! to try to stop him, to no avail. But the knight won't get there in time- the man disappears into a corridor, and Childe joins Aether, looking a little frustrated.]

Prince, [he says, trying to keep a cheery demeanor in front of the crowd,] who exactly was that? I saw your interaction from over there, and needless to say it didn't seem...pleasant.