He is considered one of the most legendary young actors in Hollywood. Almost 30 years ago, River Phoenix died of a drug overdose at the age of 23. Now his mother Heart Phoenix (78) has reminded her eldest son in an emotional post on Instagram – on the day he would have celebrated his 53rd birthday.

"August 23, 1970, one of the most incredible days of my life," she wrote alongside a picture showing young River Phoenix with his guitar. "Just as he tried to win over most people, he won over his siblings with his humor, wisdom, genuineness, talent, passion, vulnerability and undying love. He was - and still is - our greatest teacher."

The greatest pain she has ever felt, Heart Phoenix continued, was the natural birth of her children and, while completely different, "the pain of the death of my son."

"There are no guarantees in life and I don't think any of us have ever been given a promise not to have tragic moments," said the late actor's mother. River's life and death taught her to live in the now. "I'm in awe that he's still very much alive in me," the 78-year-old closes her post and thanks for the many messages she's received since her son's death.

River Phoenix collapsed after a drug overdose on Halloween night outside the West Hollywood nightclub Viper Room, part-owned by Johnny Depp, 60. In the hospital, only his death could be determined.