A woman whose sister died in the World Trade Center attacks was in court yesterday in a fight to adopt the 14-year-old niece she has raised since 9/11 — a battle that took a sudden twist when the child became a millionaire.

Challenging the aunt for the past nine years has been the girl’s Manhattan banker father, who initially denied paternity and later gave up custody rights — but had a change of heart after the child was awarded $2 million from September 11th Victim Compensation Fund.

The messy case began after the girl’s mom, Catherine Gorayeb, a 41-year-old marketing director, died in Windows on the World.

She left a 2-year-old girl, the result of a fling with Edward Kranz, according to court papers.

After the attack, Gorayeb’s sister Claire — who was three months pregnant with her own child — moved from Boston to New York to raise the toddler.

With the help of nearly $2 million from the 9/11 victims fund, she bought an Upper West Side apartment to raise her niece and her own daughter.

She began the adoption process in 2004.

“Since the tragic death of Catherine Gorayeb on Sept. 11, 2001, Claire A. Gorayeb has cared for her niece and provided her a safe, loving and caring home,” her lawyer said in a court filing, according to the Web site DNAinfo.

But Kranz, 50, said in papers, the girl’s “best interests require regular visitation rights with me, her father,” the Web site reported.

That was quite a change from his view in February 1999, when the girl was born. Kranz denied he was the father, prompting Catherine Gorayeb to file a paternity suit against him.

In September 1999, a court-ordered paternity test indicated a strong possibility the child was his.

In January 2000, the parents reached an agreement under which she gave up trying to obtain child support from Kranz and he relinquished custody and visitation rights.

He apparently had nothing to do with the girl for four years.

But in 2004, Kranz, who later filed for bankruptcy, contacted Claire Gorayeb and said he had just found out her sister died on 9/11, according to DNAinfo.

A short time later he sent his daughter a photo of himself. He later said he hadn’t made contact with her before because he was waiting until she was 5 years old.

Kranz tried in June 2004 to get custody of the child, triggering a lengthy court battle for the tragic child.

Gorayeb and Kranz have avoided speaking publicly about the messy case. Efforts to reach them yesterday were unsuccessful.

Gorayeb’s attorney, Raymond Dowd, told The Post: “This thing has been going on forever. The family has been victimized by 9/11 and by this.”