A prisoner found dead inside a Brooklyn police station this morning hanged himself with a string from his shorts, a man who identified himself as his brother said.

The 47-year-old man was taken into custody for allegedly assaulting his girlfriend, the brother said outside the Williamsburg stationhouse.

“I don’t understand why he would do something like this, he has four children. I know for a fact he would never do anything like this to himself,” the man’s distraught relative said. “I cried after I heard the news and I came here what exactly what happened to my brother.”

Cops refused to release the dead man’s name or say how long he’d been unsupervised.