SYDNEY -- The family of the late Heath Ledger spoke of their grief at losing the young actor as he was awarded a posthumous Australian film prize at an emotional ceremony late Saturday.

Ledger, who died from an overdose of prescription drugs in January, aged 28, was given the Australian Film Institute's international best actor award for his acclaimed portrayal of the Joker in "The Dark Knight."

His sister, Kate Ledger, fought back tears as she accepted the award on behalf of Matilda Rose, Ledger's three-year-old daughter with actress Michelle Williams.

"It's been without a doubt the most difficult year, losing such a loved family member," she said.

"We are so proud of him and humbly accept this award on behalf of his beautiful daughter, who we will cherish forever," she said.

Ledger's parents Kim Ledger and Sally Ledger Bell also spoke of their pride at their son's achievements.

"We are immensely proud of him, not only for his professional achievements but in the way he truly cherished his family, friends and his precious Matilda," his mother said.

"Heath was never one to accept mediocrity, he put his heart and soul into achieving what he believed was required and followed his passions with great enthusiasm and an insatiable curiosity," his mother said.

Perth-born Ledger gained international stardom and was nominated for an Oscar for his role as a gay cowboy in the 2005 film "Brokeback Mountain."

His portrayal of the Joker in the recent Batman film sequel "The Dark Knight" has been hailed by critics and has triggered talk of a rare posthumous Academy Award.

"It was this swaggering, psychopathic clown that turned his career into a legacy and the name Heath Ledger into an ongoing inspiration to actors everywhere," the Australian institute said.

"He was the untamed spirit many of us wish we could be. May the legend live on," the Australian Institute said.