You knew about Luke's secret. Him being the lightning thief, planning on betraying to camp, the whole spiel.

It was obvious that you did, Luke was your half-brother of course, and you were basically glued to his side for the first year you attended camp. And it hurt, a lot, that someone you thought you could trust, could change. Change to someone you didn't know.

Though, if there was something you learnt from him after all his pranks to other campers it was that siblings don't snitch.