Misha Defonseca, the author of a fake memoir about how she was raised by wolves during the second world war, has been ordered to pay $22.5m (£13.3m) back to her publisher.

Defonseca's extraordinary story was published almost 20 years ago as Misha: A Mémoire of the Holocaust Years. The book describes how, when she was six, the author's Jewish parents were taken from their home by the Nazis, and how she set off across Belgium, Germany and Poland to find them on foot, living on stolen scraps of food until she was adopted by a pack of wolves. She also claimed to have shot a Nazi soldier in self-defence.

The story was a huge bestseller, and was made into a film in France, but in 2008, it was found to be fabricated. The author – whose real name was found to be Monique De Wael – said that "it's not the true reality, but it is my reality", and "there are times when I find it difficult to differentiate between reality and my inner world".

She is also not Jewish, it was discovered. "Yes, my name is Monique De Wael, but I have wanted to forget it since I was four years old," she admitted in 2008. "My parents were arrested and I was taken in by my grandfather, Ernest De Wael, and my uncle, Maurice De Wael. I was called 'daughter of a traitor' because my father was suspected of having talked under torture in the prison of Saint-Gilles. Ever since I can remember, I felt Jewish."

Before the fabrications were exposed, the author and her ghostwriter Vera Lee had won $32.4 million from her US publisher Mt Ivy and its founder Jane Daniel after bringing a copyright case against them. Daniel went on to appeal the ruling, and to conduct her own research into the story, discovering documents revealing Defonseca's date and place of birth, and that rather than "running with the wolf pack", she was actually "enrolled in a Brussels school in 1943", reported Courthouse News.

Now a judge has ruled that despite the author's claims that she believed her story to be true during the publication process, she will have to pay back the money she was awarded, which amounts to $22.5m.

"The present case is unique. The falsity of the story is undisputed," wrote the judge. "Under oath, Defonseca averred that, notwithstanding her present understanding that her story was false, she believed throughout the book production process and trial underlying Mt Ivy I that her story was true; her parents were in fact taken away when she was four years old and murdered in Nazi concentration camps."

The judge expressed "no opinion as to whether Defonseca's belief in the veracity of her story was reasonable," Courthouse News reported. "However … whether Defonseca's belief was reasonable or not, the introduction in evidence of the actual facts of her history at the trial underlying Mt. Ivy I could have made a significant difference in the jury's deliberations."