A short bibliography in English on royal bastards:

Robert Bartlett, Blood Royal: Dynastic Politics in Medieval Europe (Cambridge University Press, 2020). A thematic overview of social and political aspects of royal dynasties as they evolved in the Middle Ages, sketching the political, religious, and social contexts of ruling families in the centuries in which sacramental Christian marriage, and its correlating concepts of legitimacy and illegitimacy developed.

Sara McDougall, Royal Bastards: The Birth of Illegitimacy, 800–1230 (Oxford University Press, 2017). A careful book focusing on the key generations in which the ecclesiastical definition of legitimacy evolved, with key examples from Iberia, the Norman cultural world, and the Crusader kingdoms.

Susan Marshall, Illegitimacy in Medieval Scotland, 1100–1500 (Boydell, 2021). A book which carries the story of the evolution of concepts of legitimacy and bastardy, as explored by McDougall (above), forward in great depth in one important centralized monarchy, the kingdom of Scotland, with special attention to the “Great Cause”—the royal succession “competition” of 1291—as a watershed moment.

Chris Given-Wilson and Alice Curteis, The Royal Bastards of Medieval England (Routledge, 1984). A now-aging work cataloguing the known bastards of the English kings from the Norman Conquest to end of the fifteenth century. Reflects conventional wisdom as of publication; not systematically documented to a current genealogical standard.

Peter Beauclerk-Dewar and Roger Powell, Royal Bastards: Illegitimate Children of the British Royal Family (The History Press, 2006). This chatty book carries the bastard roster forward from the fifteenth to the nineteenth centuries, with more salacious details than in Given-Wilson and Curteis.

Sarah-Beth Watkins, Charles II’s Illegitimate Children: Royal Bastards (Pen and Sword, 2023). This newest book on this shelf explores Charles II’s fifteen known illegitimate children in nine chapters. (This ground also covered, more briefly, by Beauclerk-Dewar and Powell; both works are designed for popular readership; neither is systematically documented to a modern genealogical standard.)