The gruesome timeline into the slayings of Rob Reiner and his wife Michelle is continuing to emerge after the couple’s junkie son was nabbed for allegedly hacking them to death in their Los Angeles mansion.

Rob, a beloved 78-year-old legendary Hollywood director and actor, and his acclaimed photographer wife, 70, were found with their throats slit inside the family’s home Sunday afternoon — fewer than 24 hours after the couple got into an explosive showdown with son Nick Reiner at Conan O’Brien’s Christmas party.

As cops try to pin down exactly when the 32-year-old nepo baby allegedly knifed his parents, here’s what’s known so far about the slayings:

Nick is said to have gotten into a massive blow-up with his icon father and mom in the middle of funnyman O’Brien’s holiday party Saturday night, sources said.

The trio wound up in a “very loud argument’’ in front of other guests — possibly because Nick was back on drugs and refusing yet another stint in rehab, sources and reports said.

“They had had an argument at Conan’s holiday party, and Rob had been telling people that they’re scared for Nick and scared that his mental state was deteriorating,’’ a lifelong family friend has told The Post.

Another source told People magazine: “Nick was freaking everyone out, acting crazy, kept asking people if they were famous.”

Nick gave one partygoer — “SNL’’ alum Bill Hader — the death stare before “storming off’’ after the accused killer interrupted a conversation the comedian was having, and Hader politely told him to butt out, sources told NBC.

Several guests said they were worried about Rob’s son’s behavior and that Nick looked jittery and off-kilter, the New York Times said.

Soon after the embarrassing blowout between the parents and Nick, Rob and his wife were spotted rushing out of the ritzy shindig.

It wasn’t immediately clear when their son left the event — but video captured him exiting his parents’ home at 11:47 p.m. Saturday.

Just hours after the yelling match, a “tweaked out” Nick checked into The Pierside Santa Monica hotel with his credit card around 4 a.m. Sunday, TMZ reported.

Eyewitnesses noted that there were no visible signs he’d been in any sort of violent confrontation when he was grabbing his room key.

But when hotel staff went to clean his room after he left Sunday morning without formally checking out, they found the shower “full of blood” and blood stains on the bed, sources said.

The windows of his hotel room were also covered up with bed sheets.

Cops were alerted to the grim slaying after the couple’s daughter, Romy Reiner, a 28-year-old magazine writer and aspiring actress, discovered her parents’ bodies in the family’s upscale Brentwood home just after 3:30 p.m. Sunday.

The daughter quickly told investigators that her troubled brother “should be a suspect” because he’s “dangerous,” according to sources.

Police zeroed in on the Hollywood icon’s son around 9:15 p.m.

Footage captured Nick being cuffed near a Metro station just 15 miles from the family’s mansion.

The LAPD Gang and Narcotics Unit posted since-deleted photos of Nick, whose face was blurred out, being forced to the ground with his hands twisted behind his back.

Another snap showed law enforcement pushing him against the front of a squad car.

Nick was hauled off to the Twin Towers Correctional Facility in Los Angeles, where he was booked on suspicion of murder.

He failed to show up in Los Angeles court on Tuesday for his arraignment because he was not “medically cleared” to make the trip from jail, his lawyer said.

Nick is being held without bail till he is cleared to travel to the proceeding, which could occur as soon as Wednesday, said his high-profile lawyer, Alan Jackson.