AceShowbiz - Actress Samantha Mathis has broken her silence about the night her boyfriend River Phoenix died 25 years ago.

The "Stand By Me" star died at the age of 23 on October 31, 1993, of a drug overdose on the street outside the famous Viper Club in Los Angeles, and the "American Psycho" star, who was his girlfriend at the time and there on that tragic night, has finally spoken publicly about it.

In an interview with Britain's Guardian, ahead of the 25th anniversary of his death, Mathis recalled how she thought they were only going to the club to drop off his siblings Joaquin Phoenix, then known as Leaf, and Rain Phoenix, but Phoenix announced that he wanted to stay.

"I knew something was wrong that night, something I didn't understand," she admitted. "I didn't see anyone doing drugs but he was high in a way that made me feel uncomfortable - I was in way over my head... Forty-five minutes later, he was dead."

She later added, "I knew he was high that night, but the heroin that killed him didn't happen until he was in the Viper Room. I have my suspicions about what was going on, but I didn't see anything."

The actress, now 48, went to the bathroom that night and when she came out, she thought she saw her boyfriend in a scuffle with another man and being kicked out of a side door by a security guard. When she went outside, she saw Phoenix drop to the pavement and start convulsing. She ran back inside the club and got his siblings, and Joaquin called an ambulance. Phoenix was pronounced dead in hospital, from an overdose of cocaine and heroin.

Mathis says he was sober during their relationship as far as she knows, "but I was very young then. In the days before he died, though, I knew something was going on."

She hasn't spoken about the tragedy in detail to anyone except her therapist, but decided to open up after the Guardian approached her shortly after she had watched "The Thing Called Love", Phoenix's last completed film, in which they co-starred.