Nick Reiner threw “terrifying” tantrums as a child that escalated when he struggled with drug abuse before he was charged with murdering his mother and his Hollywood icon father, Rob Reiner, according to a family friend who has known him his whole life.

The outbursts were so violent that Nick Reiner often had to be physically held back by his father, with the unidentified lifelong friend telling the Daily Mail of seeing “so much anger in his eyes” even as a kid.

Many of the family fights “had to do with [Nick] just doing something self-destructive, and fighting back when they tried to help him,” the friend said of his dad and mom, Michele, who was also stabbed to death Sunday.

“It did get physical sometimes — I’m not talking punches, but restraining him.

“I was over there, it must have been early 2000s because he was about 11, and he was throwing the biggest tantrum, and [Rob] Reiner just had him in a bear hug to restrain him,” he continued.

“The tantrum was over nothing, but he had so much anger in his eyes. It was terrifying really.

“And this happened a lot, and he never outgrew it. He had tantrums in his 20s.”

The friend, who had spoken with Nick’s grieving older brother, Jake, this week, believes that Reiner, 78, and Michele, 70, “babied” their son, who spent most of his life in and out of drug rehab programs.

Nick Reiner is accused of stabbing his father and mother to death at their Brentwood mansion over the weekend, following an uncomfortable yelling match with his parents at Conan O’Brien’s Christmas party.

Rob Reiner’s slain body was discovered by the couple’s 28-year-old daughter, Romy Reiner, on Sunday afternoon after she had been alerted by a massage therapist that her parents had missed their appointment. She called police — who later located Michele, who had also been stabbed to death.

Nick was arrested Sunday night about 15 miles from his parents’ home.