A Delaware wife was “lying in wait” with binoculars and a wig before she carried out a murder-suicide that left her husband’s lover dead, police said.

New details have emerged in the grisly slaying Monday night in which Jennair Gerardot fatally shot Meredith Chapman before taking her own life, NPR reported.

“She was lying in wait, and she shot her as soon as she walked in,” Radnor Township, Pennsylvania, Police Superintendent William Colarulo said. “And then she shot herself.”

Police said that the incident was a “calculated, planned attack” involving 48-year-old Gerardot taking a train from Delaware to kill 33-year-old Chapman at her home in Radnor Township.

Gerardot was reportedly upset that Chapman was romantically involved with her husband at the time of the murder.

Authorities said the jilted wife brought binoculars, wig, extra clothing and rubber gloves to the residence. She also came armed with ammo and a revolver.

Investigators suspect Gerardot broke a glass pane to get into the house — then cleaned up shards so Chapman wouldn’t know someone was inside.

Upon returning home, Chapman was shot dead as she entered the kitchen, according to police. Gerardot then turned the gun on herself and died just feet away from her husband’s lover.

Chapman, who was separated from her husband, recently moved to the neighborhood and started a job at Villanova University. She previously worked at the University of Delaware along with Gerardot’s husband.