According to my humble investigation skills i think the brother and the uncle were together in the past cuz Seunghyun's brother knew who Chaejun was when he was a little, same thing for the uncle he recognized who Seunghyun was, which obviously means that also the uncle and the brother knew each other before. the uncle's type is similar to his nephew and the brothers looks alike moreover the brother has natural brown hair, i also remember the panel where the brother was crying in the past which probably because they broke up.
this is my theory too. i’ll add that i think they broke up because yuseung wanted to focus more on his school or career so that he could finally be on his own and have seunghyeon live with him. like the moment we saw him crying was after seunghyeon’s conversation with little chaejun so if they really broke up there, their break up has nothing to do with what happened with chaejun. or that added fuel to the fire after.











It's been years daddy