Benjamin Herman, of Hook, Hampshire, is charged with three counts of indecent assault on a girl under the age of 13 in the early 1970s, when he was serving as equerry to Prince Philip.
The 79-year-old is also charged with one count of indecency with a child.
Mr Herman pleaded not guilty to the charges at Kingston Crown Court.
The count of indecency with a child relates to a claim he incited the same girl to commit an act of gross indecency between January 1972 and January 1974.
The assaults are alleged to have happened at a house in south-west London used by military personnel, where Mr Herman was living at the time.
He was a serving major in the Royal Marines on secondment as equerry, handling the Duke's private matters and engagements.
He has been bailed and a trial date has been set for 18 May next year. The case is expected to last two weeks.
A former personal assistant to the Duke of Edinburgh has denied four counts of historic sex abuse against a young girl.