Mandy Patinkin "wailed and cried" for hours on the night he learned of Rob Reiner's tragic death.
The legendary actor-director, 78, was found dead alongside his wife Michele Singer Reiner, 70, at their home in Los Angeles on 14 December. Their son Nick, 32, has been charged with two counts of first-degree murder.
In a special titled CBS News: Rob Reiner - Scenes from a Life which aired on Sunday, Mandy paid an emotional tribute to the filmmaker, whom he worked with on the 1987 classic, The Princess Bride.
Recalling how he discovered the shocking news, the actor-singer shared how he couldn't stop crying.
"I heard this news at about 11-something on Sunday night. I was in bed. I was in shock. I didn't sleep at all. I just kept wailing and crying," he recounted. "I didn't know what to do. I didn't know how to process it. I still don't know how to process it and I'm not looking for how to process it."
Mandy went on to explain how he believes Rob and Michele's spirits live on.
"I believe that we can connect with Rob and Michele, and every time we're thinking about this or talking about it or anyone tells a story, he's here. He will not be forgotten," the 73-year-old continued.
Elsewhere in the interview, the Homeland actor remembered the advice Rob gave him on the set of The Princess Bride, in which he played the iconic character of Inigo Montoya.
"Rob worked hard to try to get me to be the best human being I could be," he stated, beginning to tear up. "One time he said to me, 'I just wish you could get out of your own way,' and I haven't been able to achieve that to this day, but I won't quit trying. He cared about my nature. He showed it to me over and over again."
Rob and Michele wed in 1989 and also shared son Jake and daughter Romy.
Previously, the filmmaker was married to director Penny Marshall from 1971 to 1981, and he adopted her daughter, Tracy Reiner, during their relationship.
Rob also helmed movies like 1984's This Is Spinal Tap, 1986's Stand by Me, 1990's Misery and 1992's A Few Good Men.
He released his final film, Spinal Tap II: The End Continues, in September.
In addition to Mandy, the likes of Kathy Bates, Annette Bening, Albert Brooks, Michael Douglas, Kiefer Sutherland, and Jerry O'Connell also celebrated Rob's life and legacy in the special.
