Conan O’Brien reportedly stopped guests from calling 911 on Nick Reiner at his holiday party over the weekend.

Hours before Nick’s parents, Rob and Michele Singer Reiner, were found dead at their Brentwood home in Los Angeles, the couple attended the star-studded bash with their troubled son.

“They got in an argument, the father and son [at the party]. It got so bad and loud [that] someone wanted to call the police to report it,” an insider told the Daily Mail Friday.

“But Conan stepped in and said, ‘It’s my house, my party, I’m not calling the police.’ He talked them out of calling the police.”

A second source echoed those statements, noting that some guests worried that Nick needed to be placed on a psychiatric hold due to his behavior.

“When the s–t was hitting the fan, somebody said, ‘We need to call the police.’ The conversation was about getting this kid put into a mental-health hold,” the source told the outlet.

“It makes sense; who wants the cops showing up creating a scene? But the argument between Rob and Nick was pretty intense.”

A rep for O’Brien did not immediately respond to Page Six’s request for comment.

During the party, Rob reportedly told some friends that he was “petrified” that Nick could “hurt” him.

A source who allegedly attended a gathering for Rob and Michele on Monday told Daily Mail that guests were left in tears after an unspecified A-lister recalled the “All in the Family” star’s last words at the party.

“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 celeb alleged Rob said.

As previously reported, a source confirmed to The Post that Nick and his parents were involved in a massive verbal spat at O’Brien’s party on Dec. 13, just one night before Rob and Michele were found stabbed to death in their Los Angeles home.

According to multiple outlets, Nick was not only feuding with his parents but also acted erratically with some of the other partygoers in attendance that night, including comedian Bill Hader.

“Nick was freaking everyone out, acting crazy, kept asking people if they were famous,” an insider told People, with another source sharing with Us Weekly that Nick behaved “creepily” at the fancy party.

Sources told The Post that the couple’s slain bodies were eventually discovered on Sunday by their daughter Romy Reiner.

They were found with stab wounds to their throats, along with other wounds found throughout their bodies. Rob was 78 and Michele was 70.

On Wednesday, the Los Angeles County Medical Examiner’s Office revealed that Rob and Michele’s official causes of death were listed as “multiple sharp force injuries.”

The manner of death for both was listed as a homicide.

Nick was arrested later that evening and is now facing two counts of first-degree murder for his parents’ deaths.

He made his first court appearance since his parents’ deaths on Wednesday, where he received a Jan. 7, 2026, date for an arraignment in his case.