An argument between a bickering couple boiled over when an Arizona woman fatally mowed down her boyfriend, police said.

Shelly Shears, 51, was arrested by Casa Grande police after they found 59-year-old victim Billy Stephens lying near a roadway of West Saguaro Street in serious condition around 8:30 a.m. Saturday.

He suffered “significant trauma” and later died from his injuries after he was flown to a Phoenix hospital, police said.

“Detectives discovered significant evidence to determine Shears and Stephens were in a verbal argument prior to her striking him with her vehicle,” police said in a statement.

Shears remained at the scene before she was apprehended, police said.

She was booked on second-degree murder charges, Casa Grande authorities said.

She’s being held at Pinal County Adult Detention Center, and the case was sent to the county attorney’s office for review.