The sudden death of actor Philip Seymour Hoffman on Sunday from an apparent drug overdose shocked friends and associates despite the actor's struggles with drug abuse.

Hoffman, 46, was pronounced dead in his bathroom with a needle full of heroin stuck in his arm, sources tell FOX411.

“The Master” star had reportedly been sober for 23 years up until a relapse last year after which he spent 10 days in a rehabilitation facility.

“He was always quite intense, a little bit paranoid and troubled. Addiction was always going to be a constant struggle for him but this is so unexpected,” a source close to Hoffman told FOX411. “He was an incredibly knowledgeable person and so concerned with problems and issues around the world. He was one of those people with such an awakened mind he couldn’t switch off.”

Another source who saw Hoffman routinely and just prior to his death, described him as a "super friendly, normal guy" and never acted or wanted to be treated with any semblance of "star status."

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    An addiction specialist told us Hoffman's short stint in rehab may not have been enough.

    “Clearly he has had problems in the past. Last year he did a 10-day detox, and while that addresses the physical aspects, it does not get to the unresolved issues that underlie and addiction,” said Dr. Damon Raskin of Cliffside Malibu.

    Hoffman is survived by his partner of 15 years, Mimi O’Donnell, and three young children.

    “We are devastated by the loss of our beloved Phil and appreciate the outpouring of love and support we have received from everyone,” the family said in a statement on Sunday. “This is tragic and sudden loss and we ask that you respect our privacy during this grieving. Please keep him in your thoughts and prayers.”

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