Ms Wang, known for her pigtails and exuberant dress-sense, will now have to hand back at least part of her $2.4bn fortune, to her father-in-law.
In-laws' legal fight
Both Teddy Wang's father and wife claimed to be his sole beneficiary
The legal fight was over his property fortune
Ms Wang said he wrote a new will a month before he was kidnapped, never to be seen again
The elder Mr Wang said that was a lie
The case has captivated Hong Kong because of its mix of high-finance, sex and deceit.
The court ruled that a 1990 will that appeared to have been hand-written by her husband Teddy, and which left everything to Nina, was falsified.
One month after the will was written, Teddy was kidnapped and has never been seen since.
In 1999 he was declared legally dead and his father, Wang Din-shin, began legal action to recover his son's estate.
Mr Wang, now 91, stands to receive about $128m under the ruling.
Ms Wang will hardly be left penniless.
Since Teddy's disappearance she has built up his property company, Chinachem, into one of Hong Kong's largest privately-owned companies.
It was not clear how the ruling would affect her position within the company.
The case revolved around three wills.
The first was written in 1960 and would have split Teddy Wang's estate equally between his father and Nina.
In 1968, following allegations that Nina had had an affair, Teddy changed his will and left everything to his father.
This will is now seen as legally valid.
The 1990 will claimed to carry the signatures of Teddy and a witness, Tse Ping-yim.
Appeal due
But the judge, David Yam, wrote in his 558-page verdict: "I have no doubt that the questioned signatures of Wang and Tse are forged signatures and the 1990 documents are forged documents."
Lawyers for Ms Wang said she was surprised by the outcome and would appeal.
The judge said the will provided by Ms Wang was suspicious.
"Why should Teddy make a home-made will instead of making a proper will by solicitors as he had done before in 1960 and 1968?" Justice Yam asked.
The judge also questioned a phrase in one part of the will which read "One life one love".
"Why should Teddy make Document D with the words 'One life one love' when the evidence before the court suggested that Teddy was not a romantic person at all?" the judge asked.