Heath Ledger's Father Says Sister Warned Actor About Mixing Drugs

Kim Ledger recalls his famous son's last words to his family.

Heath Ledger's sister Kate was one of the last people to speak to the actor before he died at 28 of a drug overdose.

The night before his death in 2008, Ledger's father Kim tells news.com.au that Kate was concerned about her brother's drug use. "The last conversation Kate had with him was this discussion about his medications and she warned him, 'You can’t mix drugs that you don’t know anything about,'" he recalls. "He said 'Katie, Katie, I’ll be fine.' Well, that’s a cavalier boy’s answer. It just put his whole system to sleep I guess."

WATCH: Heath Ledger's Sister Praises Michelle Williams for Giving Daughter Matilda a 'Normal' Life

Ledger's death was later ruled accidental and the toxicology report showed "acute intoxication by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine."

Kim says his son was not a drug addict but didn't heed his sister's warning. "It was a one-off thing," he insists. "That’s what killed us, because he was warned by his sister the night before: 'You shouldn't mix what you're taking for pneumonia with your Ambien.' But most of Heath’s problems were self-induced."

WATCH: Michelle Williams Sells Brooklyn Home She Bought with Heath Ledger

The Oscar winner's father adds that he thinks his son's hectic work schedule had taken a toll on him. “He was a young guy that traveled all the time for work. Even as a 2-year-old, he hardly ever slept. He was trying to work and travel and do everything in a short space of time," Kim explains. "Heath mixed a couple of drugs together with sleeping tablets and he’s gone forever. That’s something we just have to deal with."

It's been over eight years since Ledger died, but his presence is still felt in Hollywood. Jared Leto has stepped into the role of the Joker in the upcoming movie Suicide Squad, which has inevitably caused comparisons between his performance and that of Ledger's Joker role in Christopher Nolan's The Dark Knight.

WATCH: Heath Ledger Surprises His Biggest Fan With a Kiss in Hilarious 2006 Flashback Video

"Heath did an impeccable, perfect performance as the Joker," Leto tells Rolling Stone magazine. "It's one of the best performances ever in cinema. I had met Heath before. I didn't know him well, but he was a beautiful person."

Jake Gyllenhaal has said that working with Ledger on Brokeback Mountain had a significant impact on his life. "I think losing Heath and being a part of a family that was something like the movie, the movie we all made together, makes you see that, makes you appreciate that and hopefully moves you away from the things that really don't matter to the things that do," he told NPR last year. "I'm trying to have relationships that are as real as they possibly can be on a movie set, be close to people because I know that it's precious."