On Tuesday, the late actor's mother Arlyn "Heart" Phoenix shared a throwback black-and-white photo of herself and River alongside a heartfelt caption that began, "On August 23, 1970, at 12:03 PM ...

River's sister Rain Phoenix also honored her late brother with a throwback photo and memorable quotes of his Frank Trapper/Corbis via Getty Images River Phoenix's family is honoring him 31 years ...

River Phoenix's family ... Mathis and siblings Joaquin and Rain Phoenix. Rain, 51, also paid tribute to her brother on social media, sharing a throwback photo of River alongside two memorable ...