Ray J and Princess Love got into a heated fight ... and we're told things were so bad, police got involved and detained Ray in the back of a squad car.

Law enforcement sources tell TMZ ... Ray J came home from a tour Thursday afternoon and he and Princess Love started fighting about their pending divorce.

We're told Princess called LAPD, claiming Ray J was being aggressive, yelling, and possibly under the influence.

Our sources say when cops arrived at the house, they detained Ray and slapped on a pair of handcuffs ... keeping him in the back of a black-and-white to de-escalate and figure out what the heck happened between them.

After speaking to both parties, we're told police determined no crime had been committed. Ray J was taken out of cuffs, released, and went on his way.

Some of Ray's interaction with police was recorded on video and posted online ... and you can hear him thank the officers for the way they handled the situation.

Ultimately, we're told police took a domestic-violence incident report ... but again, cops determined there was no crime here, and Ray J was never placed under arrest.

We reached out to reps for Ray and Princess ... so far no word back.