A Long Island man fatally stabbed his wife — and the couple’s teenage son was injured as he pried the knife from his dad, police said Tuesday.

Wayne Alcus, 49, knifed his 55-year-old wife, Patricia, to death around 7 p.m. Monday inside her Lake Drive home in Copiague in Suffolk County, police said.

The couple’s 18-year-old son, Ryan, was home at the time and discovered the bloody scene, they said. He was injured while grabbing the knife from his father, police said.

It wasn’t immediately clear if the husband and wife had any history of domestic incidents, but the couple did not live together, according to authorities.

Patricia was pronounced dead at the scene, and Ryan was taken to an area hospital for non-life-threatening injuries to his hand, police said

Wayne, who lives about eight miles away, in West Islip, was taken to Good Samaritan Hospital Medical Center for minor injuries. He was later charged with second-degree murder.

He is due to appear in Central Islip court Tuesday.