A 16-year-old Bronx teen was arrested and charged with murdering his ex-girlfriend's new boyfriend. Kevin Santiago apparently became upset when he saw ex Alma DeJesus, 16, with Michael Silva, also 16, in DeJesus's apartment building hallway on Sunday. The Daily News reports, "Santiago chased DeJesus down the hallway until DeJesus ducked and hid inside her mother's apartment...After Santiago banged on DeJesus' door, screaming for her to come out, Silva approached and ordered the ex-lover to leave." Santiago, who screamed, "Who the f--- are you?", then "turned his knife on Silva, stabbing him once in the chest." Neighbors says that Santiago had been stalking DeJesus for weeks and believe that he intended to kill her. Santiago and DeJesus (pictured) have a 7-month-old baby together.