Philadelphia Police arrested one of their own after an officer allegedly assaulted his female partner while on-duty. And investigators believe it wasn't the first time the officer struck the woman.

Police Commissioner Charles Ramsey suspended Officer Kenneth Allen after police internal affairs arrested the three-year veteran of the force Thursday afternoon.

Investigators said that Allen, 24, assaulted a female officer Friday. After an internal investigation, police found out that Allen allegedly hit the same woman on at least three other occasion, police said.

Earlier this week, Lt. John Stanford told NBC10 that two 18th District officers got into an argument Friday near police headquarters while they were both on-duty and in uniform. The argument ultimately escalated into a fight.

Sources with knowledge of the incident told NBC10 the two officers were having an affair. According to investigators, the female officer, who has worked in the department for nearly 20 years, suffered facial injuries, including fractures and bruising, and was treated at a local hospital.

The male officer, later identified as Allen, was placed on desk duty as internal affairs investigated.

"Any time you have a situation like this it's something very serious," Stanford said. "The department looks at it in a very serious way. It's not going to be something taken lightly."

Police charged Allen with four counts each of aggravated assault, simple assault and reckless endangerment. He also faces related counts.

Ramsey said he intends to fire Allen after a 30-day suspension.

