A 70-year-old man was killed after a fire was intentionally set inside his Brooklyn apartment, police said Saturday.

Cops took a 65-year-old woman found in the first floor apartment into custody on suspicion that she started the fire, a police source with knowledge of the case said.

Firefighters were called to put out the smoky blaze on Monroe St. near Throop Ave. in Bedford Stuyvesant at about 11:15 p.m. Friday.

When the fire was extinguished, they found the victim dead in the bedroom. His name was not immediately released as cops try to locate family members.

The was also found in the apartment suffering from smoke inhalation. She was taken to Woodhull Hospital where she is expected to survive.

FDNY fire marshals called to the scene determined the blaze was intentionally set.

Detectives were questioning the woman Saturday. No charges were immediately filed.

The relationship between the man and the woman was not immediately clear Saturday.