Duuuuuuuuude are you being serious here?!?! Oda gave us SO many hints! Luffy crying continuously, that royal outfit he has, the fact that he says he wanted to be there (hint - marineford to save ace), the fact that luffy became sure that ace's fruits' responsibility is in good hands now, those three cups at the end (they shared sake cups to become bros) and finally luffy uttering 'i can't believe he was alive' while crying. Those are a LOT of hints lmfao.