Joan of Arc’s surname in the modern French form is d’Arc.
The form d’Arc is a later conventional surname associated with Joan and her family. During her lifetime, names were not used in exactly the same standardized way as modern surnames, and Joan was often identified by her birthplace, Domrémy, or simply as the Maid.
Her family was also known by forms related to her father’s name, Jacques d’Arc. After Charles VII ennobled the family in 1429, the family name became associated with the noble designation du Lys. These variations explain why historical documents and modern reference works do not always present Joan’s name identically.