Rob Reiner's son Nick Reiner had "always been hostile and volatile" toward his family before he was arrested over claims he murdered his parents, sources exclusively tell Us Weekly. "Nick's problems have been going on for so long, so while everyone is in a state of shock right now, it's not entirely surprising," sources close to the situation tell Us. "A lot of his anger was directed at his parents for many, many years," the insider explained. "They did everything a parent could possibly do to help him. Even in his younger years, they really tried to get him help. And then it became a cycle of seeking treatment for him, kicking him out, or him leaving the house, him moving back in." The source said, "This went on for years." Rob and Michele Reiner's Son Nick Reiner Arrested After Parents' Murders The source said Nick's hostility and volatility weren't just directed at his parents, Rob and Michele Reiner, but his siblings, too. Rob and Michele, who wed in 1989, shared three kids: Nick, son Jake and daughter Romy. Rob had a second daughter named Tracy, whom he adopted with his ex-wife, Penny Marshall. "Romy has been so traumatized by Nick's behavior. She has always been so close with her parents, and watching their constant pain over Nick has impacted her and the whole family so much," the source told Us. Michael Buckner/Getty Images "It's been so much of their life. Rob and Michele were honest about their struggles with Nick, and those who spent time with the family saw it firsthand," one source revealed. "Everyone who knew them and loved them is struggling right now, because it was never a secret." The insider explained that Rob and Michele's friends are thinking, "What could we have done to help or to prevent this?" Another source told Us that people who grew up with Nick around Los Angeles are not surprised by his arrest. Maria Shriver Says Rob Reiner and Michele Were 'Good Parents' Before Deaths "It didn't feel like an 'if' but only a matter of 'when' something catastrophic would happen," one source told Us. As Us previously reported, Nick was arrested on Sunday, December 14, on murder charges. He is currently behind bars at a Los Angeles County jail. LAPD revealed Nick is being held on no bond. Over the years, Nick spoke out about his issues with addiction. In 2016, Nick spoke to People about being homeless for a period of time due to his problems. Romy Reiner Shared Sweet Photos With Dad Rob 2 Weeks Before His Death "I met crazy great people there, so out of my element. Now, I've been home for a really long time, and I've sort of gotten acclimated back to being in L.A. and being around my family. But there was a lot of dark years there," Nick said. Sources told Us that Rob, Michele and Nick attended a Christmas party at Conan O'Brien's home one day before Rob and Michele were found murdered inside their Brentwood, California, home at ages 78 and 68, respectively. The insider said Nick acted "creepily" at Conan's home. "Nick was going up to people at Conan O'Brien's party, asking people if they were famous," a source told Us.