"He was 27 and had the world at his feet," his mother, Jane Badler, wrote in the caption. "But sadly he struggled with mental illness and addiction. A brilliant spark shone bright too short a time .. I will miss you Harry every day of my life."
At the time, the cause of his passing was not revealed. On Monday, the Los Angeles County Medical Examiner-Coroner's Office revealed that Hains died of fentanyl intoxication.
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Hains had appeared in an episode of American Story: Hotel and also on The OA.
"A lover of life ... a crazy , creative . Magical creature ... just on loan to spread magic .....#RIP Harrison George Hains," she wrote. "Heard you were flying around creating planets and new life forms."
He had previously spoken about his struggles with addiction in an interview with the U.K. outlet Boys by Girls. In the interview, he shared how he dealt with a sleeping disorder and eventually found his way into sleeping pills.
"Maybe I have a part of me that is self-destructive, because I think I do have that," he said. "Growing up I had a very serious sleeping disorder called Idiopathic Insomnia. I couldn't sleep for my entire childhood until I started taking sleeping pills at 12/13. So I was tortured by sleep deprivation and I had a lot of phobias."
He continued by saying all of it came full circle from when he was younger and had come back to "haunt" him.
"Having my childhood so disrupted came back to haunt me in ways that were unexpected and left me with my own kind of issues that were then self-inflicted and self-destructive," he explained. "But tragedy can come in all forms. All experience is relative, all happiness is relative, all tragedy is relative. We all suffer as much as each other, there are just certain things that trigger us."
Along with American Horror Story and The OA, Haines also had appeared in The Deleted, Lulu, and The Surface. He was set to appear in some upcoming works that had not begun filming, The Mangled (filming), Xtra Life and Klowns.