Rob and Michele Reiner‘s son Nick has been arrested and is being held on $4 million bail, TMZ has learned.

The 32-year-old is in the custody of the Los Angeles County Sheriff’s Dept. as of Monday morning, according to online records. He was booked at the LAPD jail.

As we reported … the couple was found by one of their daughters Sunday with their throats slit inside their Los Angeles home.

Friends and collaborators, Billy Crystal and Larry David, were seen leaving the couple’s home Sunday evening looking very distraught.

An outpouring of tributes have come in following the tragedy, including those from Barack Obama, Stephen King, and Ben Stiller, among others.

Hollywood and fans are reeling over the killing of Rob Reiner and his wife Michele … and the family is speechless, finding it difficult to comprehend the news.

TMZ broke the story … the legendary actor-director and his wife were slain in their Brentwood home Sunday … and we’ve learned the couple’s son Nick was in law enforcement custody as of Monday morning, being questioned about their deaths.

Tracy Reiner — Rob’s adopted daughter from his marriage to ex-wife Penny Marshall — told NBC News she had just seen her father the day before for a family gathering.

The actress — best known for her role in “A League of Their Own” — told the outlet … “I came from the greatest family ever. I don’t know what to say. I’m in shock.”

TMZ broke the story … Rob and Michele suffered lacerations consistent with knife wounds, and LAPD’s Robbery Homicide Division is investigating the case.

Billy Crystal and Larry David showed up Sunday night at the house of their longtime friend Rob Reiner, who was stabbed to death with his wife Michele, allegedly by a family member.

TMZ obtained photos of Billy arriving at the Brentwood home of Rob and Michele after the couple’s throats were slit by a family member, possibly after a heated argument, according to sources with direct knowledge of the case. PEOPLE reported their son, Nick, is being questioned by police. LAPD’s elite Robbery Homicide Division is investigating the double homicide.

As you can see, Billy and his wife, Janice, appear sad and emotional, with Janice wiping tears from her eyes as the two left the area around where police roped off the crime scene. One neighbor told ABC7 that Billy looked as if he was about to cry.