MASTIC BEACH - Police and homicide detectives say a 13-year-old fatally stabbed his mother's ex-boyfriend yesterday morning after the man broke into their home, armed with a gun.

Authorities say 48-year-old Norman Shields broke into 31-year-old Natasha Bivens' home on Selden Road in Mastic Beach just before 4 a.m., then confronted her and her new boyfriend.

Police say Shields pulled out a gun and started beating Bivens. Then, they say Bivens' 13-year-old son grabbed a kitchen knife and fatally stabbed Shields.

Officials say the teen's 4-year-old sister was asleep in the house at the time.

While no official decision has been made, police say it is unlikely that the teen will face any charges.