Harvey III, Lord of Léon

He became Lord of Léon after his father's death around 1218. His fief was the castle of La Roche-Maurice.

He married Margaret of Châteauneuf, a younger daughter of Hugh IV of Châteauneuf, Lord of Châteauneuf-en-Thymerais, and Eleanor of Dreux, a sister of Peter Mauclerc, Duke of Brittany jure uxoris. After her elder brother's death, Margaret inherited one third of the Lordships of Châteauneuf, including the castles of Châteauneuf and Senonches. Harvey was also Lord of Noyon-sur-Andelle.

He died in 1240 and was buried in the Abbaye Notre-Dame de Daoulas.

Harvey III and Margaret had three children:

• Harvey IV, who succeeded his father as Lord of Léon and Noyon-sur-Andelle, and his mother as Lord of Châteauneuf;
• Alan of Léon, whose son Francis is said to have married the heiress of the Kermavan family;
• Catherine of Léon, who married Juhel of Avaugour, younger son of Henry II, Lord of Avaugour and Margaret of Mayenne.

• Chaillou, Léa. The House of Léon: Genealogy and Origins. Foundations: The Journal of the Foundation for Medieval Genealogy, volume 11, 2019, pp. 19–48 ISSN 1479-5078
• Patrick Kernévez and Frédéric Morvan Généalogie des Hervé de Léon (vers 1180-1363). Bulletin de la Société archéologique du Finistère, 2002, p 279-312.