FitzClarence

Fitzclarence or FitzClarence is a pseudo-Anglo-Norman name meaning "son of Clarence"—it usually refers to a bastard son of a Duke of Clarence, or a descendant thereof, and was used by them as a surname.
The FitzClarence family was an illegitimate branch of the House of Hanover. Prince William, Duke of Clarence, and future king William IV of the United Kingdom, had at least ten children with his mistress Dorothea Jordan, all of whom took the surname FitzClarence. All of whom were also granted by their father the rank of a marquess' younger sons or daughters.