Heath Ledger died as the result of an accidental overdose of prescription drugs the chief medical examiner for New York concluded on Wednesday.
A spokesperson said the 28-year-old, who was found dead in his Manhattan apartment in January, passed away "as the result of acute intoxication by the combined effects" of six different medications.
The actor's father, speaking from the actor's Perth hometown, said: "Our son's beautiful spirit and enduring memory will forever remain in our hearts. While no medications were taken in excess, we learned today the combination of doctor-prescribed drugs proved lethal for our boy."
"Our family enjoyed an extremely happy two week visit with Heath just prior to the New Year," he remembered. "Those recent precious days will stay with us forever… We knew Heath as a loving father, as our devoted son, and as a loyal and generous brother and friend."
He then paid tribute to the thousands of well-wishers who've offered their sympathy to the family. "Families rarely experience the uplifting, warm and massive outpouring of grief and support as have we, from every corner of the planet. This has deeply and profoundly touched our hearts and lives. We are eternally grateful."
The star's two-year-old daughter Matilda and her mum, Heath's Brokeback Mountain co-star and former girlfriend Michelle Williams, are currently in Australia with Heath's family ahead of a private funeral expected to take place this weekend.