William's style and title in full is His Royal Highness Prince William Arthur Philip Louis, Duke of Cambridge, Earl of Strathearn, Baron Carrickfergus, Royal Knight Companion of the Most Noble Order of the Garter Knight of the Most Ancient and Most Noble Order of the Thistle Personal Aide-de-Camp to Her Majesty The Queen
William's more formal style
"William hath the Title of Grace, and being writ to, is stil'd, most High, Potent and Noble Prince: And Dukes of the Blood are stil'd, most High, most Mighty, and Illustrious Princes." "Dukes are usually stil'd by the King or Queen our Right Trusty and Right entirely Beloved Cousin, and when of the Privy Council, then with the Addition of Counsellors."
William's more formal style
"William hath the Title of Grace, and being writ to, is stil'd, most High, Potent and Noble Prince: And Dukes of the Blood are stil'd, most High, most Mighty, and Illustrious Princes." "Dukes are usually stil'd by the King or Queen our Right Trusty and Right entirely Beloved Cousin, and when of the Privy Council, then with the Addition of Counsellors."