Article I
Section 9
Clause 8
No Title of Nobility shall be granted by the United States: And no Person holding any Office of Profit or Trust under them, shall, without the Consent of the Congress, accept of any present, Emolument, Office, or Title, of any kind whatever, from any King, Prince, or foreign State.
The Peerage Duke of Sussex was granted to Prince Harry via Letters Patent issued by The Queen. Megan Markle’s title of Duchess of Sussex is a courtesy title only. Nothing was granted to her, it’s a fancy version of “Mrs.”