An eyewitness claims she saw Prince Andrew and Virginia Roberts Giuffre the night they allegedly had sex for the first time — and now she plans on telling the FBI everything she knows, her lawyer said.

Attorney Lisa Bloom said she represents the witness, who wasn’t identified but was allegedly present at London’s Tramp nightclub in 2001.

“She saw Prince Andrew with Virginia,” Bloom said in an interview Tuesday with ITV’s “This Morning” show. “She remembers it vividly because she was told this is a member of the royal family. It was a very big thing to her.”

Bloom said her client was “shocked” by what she saw at the club.

“I’m going to take her to the FBI, they can investigate her claims and I call on other witnesses to come forward,” the lawyer said. “Now is the time. People are in fear, of course, of a powerful royal family, but women have to stand with other women.”

Giuffre has claimed that Jeffrey Epstein and his then-girlfriend, accused madam Ghislaine Maxwell, took her to Tramp to meet the Duke of York for the first time. She has said the two had sex three times beginning when she was just 17.

Tramp is where Giuffre says the royal “was sweating all over me” as they danced — a key detail that Andrew has bizarrely denied.

Bloom — whose famous lawyer mom, Gloria Allred, represents a number of alleged Epstein victims — called on Andrew to help in the ongoing investigation into Epstein’s alleged sex-trafficking ring.

“Let’s put those words into action, Prince Andrew. You said you were going to cooperate. Let’s do it,” she said. “Don’t make us subpoena you, don’t make law enforcement chase you down. Come to the US, sit down with the FBI and with victim’s attorneys like myself.”

Andrew has steadfastly denied Giuffre’s claims, saying he can’t remember meeting her.