More details on crazy father-son bash of 10-year-old!

Fort Greene’s biggest bully was arrested for beating up a 10-year-old boy last week — and this time, the perp is a parent.

Jesus Powell, 29, was picking up his son outside of PS 20 — on Adelphi Street between Willoughby and DeKalb avenues — at about 3 pm when he spotted another student with whom his son had been feuding.

That’s when Powell allegedly grabbed the 10-year-old kid, pinned the child’s arms behind his back and then ordered his son to take a few free swings.

After his son was finished throwing haymakers, Powell allegedly landed the final blow and left the poor boy with a bruised face.

But Powell didn’t stop there, according to police records. He chased the battered child straight to the principal’s office, where he threatened both the child and a school administrator.

It’s unclear what action the school took after that — PS 20 staff won’t comment on the attack — but cops arrested Powell three days later. He was freed after his first court hearing on Dec. 10, pending child assault and menacing charges.

School officials apparently kept the assault under the community radar, too, because parents were miffed to hear about the attack from reporters this week.

“I had no idea. I’m moving my child to another school,” said Jose Morales, father of an 8-year-old girl at PS 20. “This is what the principal always does here after bad things happen — nothing.”

An official with the Department of Education said that Powell voluntarily transferred his kid to another school — though it’s unclear which — and that “horse-playing is not acceptable behavior.”

The incident marks another sad-face sticker for PS 20. Last year, former principal Sean Keaton was arrested for allegedly punching and kicking the school’s teacher union rep during a disciplinary hearing.

— with Thomas Tracy