An elderly man attempted to leave half of his $1.25 million estate to a daughter he believed he had fathered decades earlier but had never met.

Ian Roderick Douglas died at Goulburn in February 2013 aged 72 and in his will, written three years earlier, he bequeathed half of his estate to his daughter Darcelle Wu and half to "my other daughter whom I have yet to find and whose name and whereabouts are unknown to me".

Mr Douglas believed he might have a second daughter who lived in Victoria but he didn't know her name. Investigations by his executors discovered the girl's mother was probably named Lily who lived in Annandale in the late 1950s and 1960s.

But efforts to track down Lily or her daughter, who would be aged about 50, were unsuccessful. Adverstisements were placed in Victorian newspapers, including regional newspapers, asking anyone with knowlege of any daughter or grandchild of Mr Douglas to come forward. No response was received.

Kathleen Stuchbury, who lived next door to Ms Wu's uncle Kenneth Ross in Annandale in the 1950s and 1960s, had some information about a Lily but Ms Stuchbury died in 2012.

Ms Wu, who was born in 1964, only learnt that Mr Douglas was her father when she was 17 and they did not meet until 1990.

Ms Wu had believed her mother's husband was her father.

They did not see each other often and, a year before his death, Mr Douglas told her he had been told by someone else that he had another daughter.

He said to Ms Wu, "When I find her will you come along with me to meet her? I don't have any more information at this time, but I am going to look into it. If I find out more I will let you know and we can book some tickets to go down to Victoria."

Mr Douglas, who was unmarried and described as a "private man", dictated that, if his "Victorian daughter" or any of her children could not be found, Ms Wu should have that share of his estate.

In the NSW Supreme Court on Tuesday, Justice Richard White ordered the entire $1.25 million estate to go to Ms Wu.

But he said if Mr Douglas's other daughter or her desendants did come forward, they could seek their half share from Ms Wu.