NEW YORK (CBSNewYork) -- The NYPD is on the hunt for a grandfather who allegedly killed his granddaughter's boyfriend early Sunday morning.

Authorities said officers were called to a report of an assault with a knife at 1225 Broadway in Brooklyn around 2:15 a.m.

When officers arrived, they discovered 21-year-old Kevin Rivera with a stab wound to the chest, police said. Rivera was rushed to Woodhull Medical Center, where he was later pronounced dead.

Following an investigation, police identified 81-year-old Nicolas Diaz as a suspect.

Authorities said the victim had been arguing with his girlfriend when Diaz stepped in and stabbed him.

Anyone with information is urged to call Crime Stoppers at (800) 577-TIPS (8477). You can also submit a tip by logging onto Crime Stoppers website or text a tip to CRIMES (274637), then enter TIP577.