The future Duke of Clarence, perhaps.

It is usual within the our Royal Family for Princes to become Dukes on marriage.  Prince and Princess William became Duke and Duchess of Cambridge.  Exactly which Dukedom is announced at the time.  York has been used for second sons, but it is his Uncle's title so Harry will need another.  New Whig is tipping that Prince harry will be the future Duke of Clarence  a title held by Queen Victoria's Uncle, who was briefly William IV.