Nick Reiner, the son of legendary director and actor Rob Reiner and Michele Singer Reiner, was diagnosed with schizophrenia and on new medication that make him "out of his head" for weeks prior to his parents' murders, sources with knowledge of the situation confirmed to TMZ.

Nick, 32, was reportedly being treated by a psychiatrist but displayed "alarming" behavior in the past month after doctors switched his medication. The source said Nick became "erratic and dangerous" about three to four weeks prior to his parents being found stabbed to death in their Brentwood mansion on Sunday (December 14).

Rob Reiner reportedly told others that he was "petrified" that his son could "hurt" him prior to his and his wife's murders over the weekend. An anonymous A-list celebrity who attended Reiner's memorial service on Monday (December 15) told the Daily Mail that they spoke at Conan O'Brien's holiday party hours before his death.

“I’m petrified of [Nick]. I can’t believe I’m going to say this, but I’m afraid of my son. I think my own son can hurt me,” the unspecified source said.

Nick Reiner who was charged in connection with his parents' murders this week, reportedly wasn't invited to the Christmas party, but attended with his parents because they didn't want to leave him home alone, the Hollywood Reporter reported on Tuesday (December 17).

Nick was alleged to have “often" showed extreme and stressful behavior," which had and “grown degrees even more concerning in recent weeks," according to the report.

Rob and Michele Reiner were reportedly "reluctant to leave him home alone in the guesthouse" of their Brentwood, California, home, where he had been living under "watchful supervision."

Nick reportedly stormed off after a tiff with comedian Bill Hader at O'Brien's Christmas party Saturday (December 13) night, hours before his parents were found dead with apparent stab wounds at their home on Sunday (December 14). The 32-year-old is alleged to have interrupted Hader, who told him he was having a private conversation, which resulted in him standing still and staring before "storming off."

The Reiners allegedly got into a "very loud argument" with their son, which led to them leaving O'Brien's party. A source had previously told PEOPLE that Nick Reiner was acting erratically at the party.

“Nick was freaking everyone out, acting crazy, kept asking people if they were famous,” an insider told PEOPLE.

Nick had publicly acknowledged his issues with drug addition and homelessness in the past. Rob and Michele Reiner were reported to also have stab wounds to multiple other parts of their bodies, sources with knowledge of the situation confirmed to the New York Post.

Reiner, the son of producer, writer and actor Carl Reiner and actress and singer Estelle Reiner, initially gained national prominence playing Mike 'Meathead' Stivic on All in the Family and is credit with numerous acting roles during a career that spanned seven decades. The New York City native made his directorial debut with the heavy metal mockumentary This Is Spinal Tap (1984) -- having released a sequel earlier this year -- which was followed up by The Sure Thing (1985), Stand By Me (1986), The Princess Bride (1987), When Harry Met Sally...(1989), Misery (1990) and A Few Good Men (1992).

Kristin Lessard & Steve Kelly