An 81-year-old man has been arrested for allegedly stabbing to death his granddaughter 's ex-boyfriend after the young couple started arguing following their daughter 's first birthday party . Nicolas Diaz reportedly intervened after his granddaughter , Amber Diaz , and her former partner , Kevin Rivera , 21 , got into a dispute at their home in Brooklyn , New York , in the early hours of Sunday . The recently separated couple , who have a baby daughter , Aeralye , together , had just returned to the apartment after celebrating the infant 's first birthday . Diaz wanted to break up the fight , relatives said . He allegedly stabbed Mr Rivera , an unemployed musician , with a knife , before fleeing the scene . When medics arrived at the Bushwick property , they discovered Mr Rivera with a chest wound . Scroll down for video . 'Manslaughter ' : Nicolas Diaz ( Ieft ) , 81 , allegedly stabbed to death his granddaughter 's ex-boyfriend , Kevin Rivera , ( right ) , after the couple started arguing following their daughter 's first birthday party on Sunday . Scene : Diaz reportedly intervened after his granddaughter , Amber Diaz , and 21-year-old Mr Rivera got into a dispute at their home in this apartment bock at 1225 Broadway ( pictured ) in Bushwick in Brooklyn , New York . He was rushed to Woodhull Medical Center , but despite medics ' best efforts , was later pronounced dead , according to the New York Times . Police immediately launched a manhunt for Diaz . On Monday morning , the suspect turned himself into police , NBC reported . He has since been charged with manslaughter and criminal possession of a weapon in relation to the killing . Miss Diaz and Mr Rivera had apparently been dating for around three years before they split . Relatives told the Times their relationship had started to break down following Aeralye 's birth last year . 'They were always fighting . Girlfriend and boyfriend stuff , ' said Jose Rivera , the victim ’ s grandfather , adding he had adopted his grandson , along with his twin brother and sister , after their father had died . Police : The pensioner allegedly stabbed Mr Rivera with a knife , before fleeing the scene . When medics arrived at the property , they found Mr Rivera with a chest wound . Above , a cop stands at the entrance to the home . Grief-stricken : Mr Rivera was rushed to Woodhull Medical Center , but despite medics ' best efforts , was later pronounced dead . Above , some of the victim 's devastated relatives are pictured hugging on the street . On the day of the alleged manslaughter , the couple had just returned home after celebrating Aeralye 's first birthday together . They were arguing when Diaz reportedly lashed out at Mr Rivera with the knife . 'The girl was screaming , ' one neighbor told the Times . 'It was getting out of control . I heard screaming , footsteps - hard . ' The neighbor said they then called 911 . Police arrived at the scene 20 minutes later . Speaking to the New York Post , Miss Diaz said of her now-deceased ex-boyfriend : 'Kevin is my ex-boyfriend and he was trying to get back with me . He wouldn ’ t leave , and he was yelling and pushing . ' Although Mr Rivera , who also suffered slashes to his arms in the attack , was unemployed at the time of his death , he had apparently considered applying to be a driver for the online taxi service , Uber . Aerlaye has reportedly been taken into custody by officials . Emergency : Miss Diaz and Mr Rivera had apparently been dating for around three years before they split . Relatives told the Times their relationship had started to break down following Aeralye 's birth last year .
Kevin Nicolas Diaz and Amber Diaz started arguing after their daughter 's party . Miss Diaz 's grandfather , Rivera , 81 , allegedly intervened with knife . He 'stabbed Mr Nicolas Diaz in the chest ' ; fled the scene after Sunday 's killing . Victim rushed to hospital with stab wound , where he was declared dead . Diaz turned himself in to police in Brooklyn , New York , Monday morning . Has been charged with manslaughter , while baby girl is now in custody .