A woman named him in documents she filed in a Florida court over how prosecutors handled a case against financier Jeffrey Epstein, a friend of the prince.
She claims that between 1999 and 2002 she was forced by Epstein to have sex with the prince when she was a minor.
In 2008, Epstein was sentenced to 18 months in prison after pleading guilty to a single Florida state charge of soliciting prostitution. He remains a registered sex offender.
The palace said it would not comment in detail on the legal proceedings.
But a Buckingham Palace spokeswoman said, "This relates to long-standing and ongoing civil proceedings in the United States, to which the Duke of York is not a party.
"As such we would not comment on the detail. However, for the avoidance of doubt, any suggestion of impropriety with underage minors is categorically untrue," she said.
