Maria Shriver is "gutted" by the deaths of longtime friends Rob Reiner and wife Michele Singer Reiner, whom she said "never stopped" being committed parents. "I loved them, and I knew they loved me, for any friend like that is such a gift," Shriver, 70, wrote via an Instagram tribute to the late couple on Monday, December 15. "They gave me and all their friends that gift all the time." She revealed, "They loved their kids so much, and they never stopped trying to be really good parents," amid news that Rob and Michele's son Nick Reiner has been arrested on suspicion of committing the murders. News broke on Sunday, December 14, that two bodies were found at Rob and Michele's Brentwood residence in Los Angeles. The LAPD confirmed at the time that Rob, 78, and Michele, 68, were found dead "from apparent stab wounds." Rob Reiner's Son Nick Held Without Bail, Police Reveal in New Statement Their family later confirmed their deaths, telling Variety in a statement, "It is with profound sorrow that we announce the tragic passing of Michele and Rob Reiner. We are heartbroken by this sudden loss, and we ask for privacy during this unbelievably difficult time." Rob and Michele shared three kids, Jake, 34, Nick, 32, and Romy, 28, in addition to the director's daughter Tracy, 61, with late ex-wife Penny Marshall. Us Weekly confirmed on Monday that Rob and Michele's son Nick - who has been vocal about his struggles with addiction - had been arrested on a murder charge, was in custody. Jamie Lee Curtis and Husband Mourn Late Rob and Michele Reiner in Tribute "My love is with their family. I'm so sad for them," Shriver wrote in her tribute on Monday. "I'm devastated, gutted, shocked, stunned, and so deeply saddened, as are all of the people who loved them and who they loved." Shriver noted that the legendary director and his wife were among her "closest friends," having raised their kids together "from mommy and me on up." She said, "We laughed together, we cried together, we played together, we dreamed together" throughout their decades-long friendship. The I've Been Thinking author recalled having dinner with Rob and Michele "this past week," saying that the couple "were in the best place in their lives: loving one another, loving their friends, their family, their country." Rob Reiner's Daughter Tracy Speaks Out After Legendary Director's Death Shriver applauded the pair for their continued efforts to make their family and the world a better place. "They never gave up on our country. They wanted to make it better," she explained. "They always, always wanted to make our world better, and they were willing to fight to make it the country they loved." Amid the tragedy surrounding their murders, Shriver said, "I hope people remember them as two deeply talented, kind, fun, loving, good, patriotic people who loved each other deeply." She concluded: "I'll miss you, Michele. I'll miss you, Rob. I love you both. Thank you for your friendship. God bless you both. Life will not be the same without you here, that's for sure. ♥️." Prior to his death, Rob was one of the most prolific entertainers in Hollywood, working as a writer, director and actor. Throughout his career he directed films including This Is Spinal Tap, Stand By Me and When Harry Met Sally and starred on hits like All in the Family.