EXCLUSIVE: How Slaughtered Rob Reiner's Daughter Romy, 28, is 'Hanging by a Thread' After Finding Director and Wife's Bloodsoaked Bodies

Romy Reiner's sanity is feared to be "hanging by a thread" after discovering the lifeless body of her movie icon father, RadarOnline.com can reveal.

Sources told us the devoted 28-year-old daughter of the When Harry Met Sally… director, 78, was first on the scene of the bloodbath at his and her 68-year-old mother Michele Reiner's mansion in Brentwood, California, after they had their throats slit as they lay in bed on December 14.

Since her brother Nick, 32, has been arrested and charged with the murders, insiders say she has "gone to pieces."

Sources now describe Romy's emotional state as "astonishingly fragile" and "beyond raw" after she discovered the scene of the double-homicide of her parents.

One claimed: "Her sanity is truly hanging by a thread. A scene like that would test even the most hardened cop or paramedic, but for someone like Romy, who has seen nothing of that side of life, it is horrifying and totally destabilizing for her mind. Add in the horrifying fact that it was her parents' bodies, and she is now teetering on the brink."

"Her family is really worried she won't be able to cope long-term with the memories of what she witnessed."

Romy made her grim discovery after she had gone to check on her parents, after their massage therapist could not reach them.

Other insiders said her older brother Jake, 34, has "had to step up" and become a "pillar of strength" for her and their family as they cope with their grief and shock.

One added, "Jake has really had to take on a fatherly role. He lives by the principle of 'family first,' which is exactly what Rob and Michele taught their children when they were alive."

Jake graduated from Syracuse University and has forged a career in journalism, presenting, acting, and podcasting.

He has appeared in the likes of Curb Your Enthusiasm, For All Mankind, and Netflix's Monsters: The Erik and Lyle Menendez Story, where he portrayed a reporter covering a shocking parental murder – a heartbreaking coincidence, but an experience some suggest has given him perspective for the current tragedy.

A source said, "Jake's calm demeanor and strong sense of duty are helping to keep the family grounded."

Nick Reiner, by contrast, had struggled for years with addiction and mental health issues, and is believed to have been battling with schizophrenia in the lead-up to the murders of his parents.

He had numerous rehab stints and is said to have clashed with his parents at a December 13 party hosted by comedian Conan O'Brien.

In a joint statement, Jake and Romy said about their parents' nightmarish deaths: "Words cannot even begin to describe the unimaginable pain we are experiencing every moment of the day. The horrific and devastating loss of our parents, Rob and Michele Reiner, is something that no one should ever experience.

"They weren't just our parents; they were our best friends. We are grateful for the outpouring of condolences, kindness, and support we have received from family, friends, and people from all walks of life."

Romy's Instagram feed is filled with pictures and videos of her with her beloved dad.

They include what is believed to be the last snap of the director, which shows him enjoying a swim in the sea with his daughter on a sun-soaked break.