A Long Island man has been jailed for allegedly attempting to kill his sister with a crossbow, a plot he had reportedly been scheming since December, authorities revealed.

Samy Sedhom, 21, shot an arrow that grazed the right side of his 28-year-old sister’s face, severing her ear and leaving her injured outside their Lawrence residence around 9:23 p.m. last Friday, according to Nassau police’s Tuesday announcement.

The troubled brother allegedly lay in wait in a vehicle across the street, targeting his sister as she returned from the gym and attempted to close the garage door, court documents indicate, as reported by WABC.

Sedhom was taken into custody on Friday. He reportedly confessed to the police that his intention was to kill his sister, a plan he had been formulating since Christmas.

Authorities discovered the hunting arrow embedded in the garage’s back wall, and also confiscated a crossbow box, a samurai sword, and a MacBook from Sedhom’s bedroom, the outlet relayed.

The injured woman was transported to a nearby hospital where she remains in stable condition, Nassau County District Attorney Anne Donnelly informed News 12 Long Island.

A “brother-sister rivalry” sparked the attack, Donnelly said, noting the siblings had been arguing over the temperature in the house.

“She liked to keep it cooler, he wanted it warmer,” she told the local news station.

Sedhom was charged with second-degree attempted murder, first-degree assault, criminal possession of a weapon in the fourth degree, tampering with physical evidence, and first-degree stalking.

He was arraigned Sunday at First District Court in Hempstead, with an order of protection reportedly issued for his sister.

He is due back in court on Wednesday.