The message recorded by Glenn Mulcaire was of the Duke arranging to leave Sandhurst to meet the now Duchess, the Old Bailey heard.
It was found on a micro-cassette in former royal editor Clive Goodman’s flat.
In it, the Duke says: “Hopefully I should be able to leave by seven at the latest.”
Later in the message he repeats: “Planning on definitely coming out by sevenish so I will be with you by eight at the latest.”
Goodman, 56, was asked about the recording, dated February 23 2006, during his third day in the witness box.
Mr Spens asked Goodman: “How did this voice message from Prince William to Kate Middleton come to be on a micro-cassette?”
Goodman replied: “This was originally recorded by Glenn Mulcaire.”
Goodman admitted phone hacking and was sentenced in 2007. He denies conspiring to commit misconduct in a public office.