Pomona police investigators still don't know what set off the fight. They say the older brother, 24-year-old Victor Aguero, appeared to be drunk.
He died in an ambulance that was en route to a waiting helicopter that would have rushed him to the hospital.
This stabbing occurred on the 200 block of Whitney Avenue in Pomona.
The teen was held without bail at Los Padrinos Juvenile Hall as the district attorney reviews the case.