Nick Reiner's spiral that allegedly led to the grisly murder of his parents began with concerns over his weight gain, according to an insider.

The accused killer was suffering from schizophrenia and detached from reality when his Hollywood icon father Rob, 78, and mother Michele, 70, were found dead in their Los Angeles home on December 14.

Nick, 32, was first diagnosed with schizoaffective disorder around 2020, TMZ reported.

He had been prescribed medication that kept his condition stable until about a month before his parents were killed.

According to the insider, Nick raised concerns with his doctors about his weight gain. Photos over the years showed his weight increased as he got older.

Weight gain is a known side effect of medication used for disorders on the schizophrenia spectrum.

However, doctors allegedly accommodated Nick's request and changed the drugs that had been stabilizing him.

The new medication triggered increasingly alarming, unsafe dangerous behavior that only worsened over time and culminated in the alleged murders, per the outlet.

Nick Reiner was suffering from schizoaffective disorder and increasingly broken from reality when he allegedly killed his parents, according to an insider

Nick, 32, had asked his doctors to changed his medication because of concerns over weight gain. The new drugs allegedly destabilized his state of mind

Rob and Michele noticed the changes in their son's behavior but were unsure of what to do.

Doctors also did not intervene by placing Nick on a temporary psychiatric hold, which could have lasted up to 14 days.

Schizoaffective disorder is a mental illness marked by symptoms such as hallucinations, delusions, mania and major depression.

Those diagnosed are prone to suicidal ideation, conflicts with family members or substance abuse, according to the Mayo Clinic.

The night before the killings, Nick attended a star-studded holiday party hosted by Conan O'Brien. His parents brought him along because they were concerned and wanted to 'keep an eye on him.'