Alan IV of Cornwall (died 1119) was duke of Brittany, from 1084 to 1112. He was also Count of Nantes and Count of Rennes . He was son of Duke Hoel II and Havise of Brittany. He was known as Alain Fergant, which in Breton means "Alan the Younger".

Alan IV had to face an invasion of William I of England and was forced to abandon his duchy in 1086. Peace was made in the same year and Alan married Princess Constance of England , William's daughter. This marriage was forced upon Alan and he is presumed responsible for Constance's death by poisoning in 1090 -- William of Malmesbury says she was killed because she was too conservative for the Breton court. Alan married again in 1093 with Ermengarde of Anjou , a formidable woman who became the real ruler of Brittany. By her he had a son Geoffrey, a daughter Havise (married to count Baldwin VII of Flanders) and his heir Conan. In 1098 Alan went on Crusade, leaving Ermengarde as his regent, and returned in 1101. Alan IV was not a popular duke and was forced to abdicate in 1112. He retired to the monastery of Redon and died there in 1119.

His illegitimate son was Brien FitzCount.

See also: Dukes of Brittany family tree