On Tuesday the Brazilian Supreme Court ruled that the boy "be handed over to his father and should be returned to the United States."
Smith said Goldman was "elated" when he heard the court's decision.
"A big smile came to his face, but he said, 'I'm not going to let my guard down until it's wheels up," Smith told the AP Tuesday.
The boy went to Brazil with his mother when he was 4, but the mother never returned to the United States. She divorced Goldman and remarried, but died giving birth to a daughter she had with her second husband.
The mother's family assumed custody of Sean and has fought Goldman's claims for custody for the past five years.
Wednesday's Supreme Court ruling came as Bianchi wrote a passionate letter to the president of Brazil, pleading with him to intervene and prevent the boy from being taken away just before Christmas.
"Our moral foundation values the mother's role. In the absence of the mother, the raising should be done by the grandmothers. This is custom in Brazil from north to south," she wrote, calling the custom "authentically Brazilian."
Bianchi claimed in her letter that she has become the "target of an international campaign of unbelievable proportions. American authorities give public declarations saying I am a kidnapper," she wrote.
The grandmother said all the legal arguments did not take into consideration what the boy wants.
"Mr. President, this is not a cry of a grandmother in agony. This is the clamor of a Brazilian fighting with all of the strength that she has left so the justice of this country would apply the laws with humanity," she said.
Bianchi said sending Sean to New Jersey would tear him away from the family he has lived with for the past five years, and from his three-year-old sister, Chiara. "To do this, especially on Christmas Eve, is inhumane," she said.
Kate McCarthy, Mark Mooney and The Associated Press contributed to this report.