(SPOILERS) nothing is shown, or even explained. it's kind of open-ended, with Mikey telling his kids that Bobby flew away, but the implication seems to be that the king killed Bobby, and Mikey just kind of wrote in a happier, more whimsical ending to tell his kids
'The King' beats the younger boy on a regular basis, and at one point violently attacks him (not shown to the audience) to the point he is sent to the hospital.