He claimed he changed the locks and replaced the rear door and went on to renovate the home and began leasing it. He spent $35,000 on the home in 1998 and a further $108,000 in 2014, according to the ABC.
According to Nine, the outcome of the appeal was due to be heard tomorrow, however the family has withdrawn its appeal against the decision, which awarded ownership to Mr Gertos last year.
The last owner of the home was Henry Downie who purchased the property in 1927 and died in 1947, according to Nine.
His family previously claimed he passed away in 1947 and didn't leave a will and they were unaware of the property until they were contacted by police.
This was in 2017 when Mr Gertos applied to be made the owner of the land using squatters' rights, under the Real Property Act. He was challenged by the last owner's family at that stage, but was ultimately awarded the deed to the Ashbury home.
Lawyer James Jordan said Mr Gertos had been "vindicated" by the findings of the Court of Appeal.
"He (Mr Gertos) offered the family a large amount of money to settle well prior to any court case and we, on behalf of Bill, told the family they had some legal problems, that the law was against them, and the family chose not to listen to us," Mr Jordan said.
He added Mr Gertos would not pursue the family for his considerable legal costs.
Mr Gertos made headlines in March this year after a confrontation with an A Current Affair reporter.
Video showed he appeared to pour a cup of coffee over A Current Affair reporter Steve Marshall's head, although he claimed Marshall "ran into" him.
During the segment, Mr Gertos also had words for the family of the deceased owner.
Mr Gertos said if he hadn't taken over the property it would have become a "rat-infested squalor".
"Why should these people be rewarded with what they say is a family estate when they couldn't care less about who died?" he said.
"They couldn't care less that their grandfather had, they don't care about their family. Maybe they do care, maybe they just never communicated, I don't know, but 70 years for God's sake."
Property records last year showed the 498 square metre, three-bedroom, one-bathroom, one car space house was most recently advertised for rent at $600 per week.