Hayden Panettiere’s peeling back even more layers of her messy family drama — revealing the shocking moment her former costar Milo Ventimiglia told her her dad had been arrested for allegedly abusing her mom.

In her memoir, “This Is Me: A Reckoning,” Hayden recalled Milo — who she dated from 2007 to 2009 — coming to her “Heroes” trailer with devastating news … letting her know that her dad, Alan Panettiere, was sitting in jail after an incident involving her mother, Lesley Vogel.

Hayden says her heart started pounding so hard she thought it might burst through her ribs … with her mind spiraling into a million questions — like who called the cops and whether the whole thing had somehow been a misunderstanding.

The actress admitted she’d sensed tension between her parents the night before at a charity event — noting how her dad looked fed up with Lesley based on his body language — but at the time, she figured it wasn’t really her problem.

Even with all the drama simmering beneath the surface, Hayden says she never thought things would allegedly turn physical between her parents. But once Milo told her to prepare to bail her dad out, she jumped straight into action — tracking down her lawyer’s number and prepared to drop tens of thousands of dollars.