Nicole Kidman's father, Dr Antony Kidman, has died after a fall in Singapore, where he was visiting his younger daughter Antonia and her children.
Singapore police said they were investigating the "unnatural" death of a man but did not give his name.
"Police were informed today at about 0954 hours [local time] that a man in his 80s was pronounced dead at Tan Tock Seng Hospital," a Singapore police spokesman said.
"Police are investigating the unnatural death," he added.
Dr Kidman was a respected clinical psychologist and researcher who had worked with the University of Technology's Health Psychology Unit at Royal North Shore Hospital in Sydney.
He was an academic in the study of the brain and nervous system and had been carrying out scientific research and lecturing for more than 30 years.
"It is with great sadness that we learn of Dr Tony Kidman's sudden passing," the university's vice-chancellor, Professor Attila Brungs said in a statement.
"During his 43 years at the University of Technology Tony has contributed greatly - as a colleague, as a researcher, and as a health practitioner.
"Tony will be missed by all at UTS. Our thoughts are with his family at this time."
One of Dr Kidman's key areas of interest was the mental health issues of young Australians, in particular psychosis, bullying and stress.
Together with colleagues, Dr Kidman was involved in providing services for young people in the delivery of appropriate treatment and clinical services.
He authored several publications dealing with anxiety and depression and was a regular speaker on television and radio.
Dr Kidman was awarded the Order of Australia for his services to health in 2005.
He and his wife Janelle recently celebrated their 50th wedding anniversary.
As yet there has been no official statement from his family.
ABC/wires