Rob Reiner’s daughter, Romy Reiner, reportedly “lived in fear” of her older brother, Nick Reiner, before he allegedly killed their parents.

“It feels like Romy has been scared of Nick since she was a child,” an insider told the Daily Mail Sunday.

“Even before his drug addiction, his outbursts were frightening because they seemed to come out of nowhere. She tried to stay out of his way as much as she could but it wasn’t easy.”

The source alleged that Romy, who will be celebrating her 28th birthday on Dec. 27, “didn’t think it was a good idea” for Nick, 32, to be living in their parents’ guesthouse.

“She didn’t even like the idea of him living across the street from her,” the insider claimed, explaining that the internet personality lived next door to her dad, Rob, and mom, Michele Singer Reiner.

“But she knew they moved him in so they could keep a close eye on him and give him a roof over his head,” the source said.

“There were plenty of times when Romy would be upset with Nick, and naturally that made her much closer to Jake.”

According to the source, Jake, 34, allegedly felt similarly about Nick, “and Romy was able to talk about it when she didn’t want to burden their parents.”

“She and Jake are numb right now,” the insider claimed.

Despite allegedly fearing Nick, Romy attempted to help her brother in the ways she could and would refer to him as her “best friend,” according to the source.

“Anytime that her parents looked overwhelmed or asked for help, Romy and Jake were there for Nick. It wasn’t perfect by any means, but she never disowned Nick,” the insider added.

A rep for the Reiner family wasn’t immediately available to Page Six for comment.

Nick was arrested on Dec. 14 in connection with the deaths of his famous parents at their Brentwood, Calif., home.

Insiders told the post that Romy found her parents’ dead bodies. She reportedly told officers that Nick should be a person of interest.

Nick, who has a history of violence and substance abuse, will be arraigned on Jan. 7.