|Duke of Brittany|
|Reign||20 November 1008 – 1 October 1040|
|Regent||Hawise of Normandy (Regent 1008–1026)|
|Died||1 October 1040|
|Spouse||Bertha of Blois|
|Issue||Conan II, Duke of Brittany|
Hawise, Duchess of Brittany
|Father||Geoffrey I, Duke of Brittany|
|Mother||Hawise of Normandy|
Alan succeeded his father as Duke of Brittany in 1008. Because he was still a minor at his father's death, his mother acted as regent of Brittany  while her brother Richard II, Duke of Normandy assumed guardianship over Brittany.
In the early 1030s Robert I successfully attacked Dol and Alan's retaliatory raid on Avranches was repulsed causing continued raiding back and forth between them. Facing an invasion from Normandy via land and from Duke Robert's fleet, Robert, Archbishop of Rouen (uncle of Hawise and Richard II) mediated a truce between his two great-nephews at Mont Saint-Michel where Alan swore fealty to his cousin Robert.
Alan III also assisted Herbert I 'Wake-Dog' in his wars with Avesgaud, Bishop of Le Mans and was with the count in his attack on Avesgaud's castle at La Ferté-Bernard destroying the castle and causing Avesgaud to flee.
In 1037, upon the death of Robert, Archbishop of Rouen, the protection of young William was now left to Alan III and his cousin Gilbert, who tentatively held Normandy together. They appointed Mauger to the now vacant see of Rouen and his brother William as count of Arques, attempting to gain their support for Duke William.
Alain and Bertha of Blois had:
- Conan II, (d. 1066), succeeded his father.
- Hawise of Brittany, who married Hoel of Cornouaille.
|Ancestors of Alan III, Duke of Brittany|
- Among the guardians Duke Robert chose to watch over his son William were at least three family members. Alan III was probably selected as both a family member and one who would not expected to compete with young William. Gilbert, Count of Brionne was another grandson of Richard I who could be counted on for military support to aid William. Also the senior member of the family was Robert, Archbishop of Rouen who lent his powerful support to the young Duke William. See: Crouch, The Normans (2007). p. 60.
- Not long after the last of young Duke William's three powerful guardians, Gilbert 'Crispin' Count of Brionne, was himself assassinated while riding with friends. See: Crouch, The Normans (2007), p. 61; and Cokayne, The Complete Peerage IV, pp. 308–9.
- Detlev Schwennicke, Europäische Stammtafeln: Stammtafeln zur Geschichte der Europäischen Staaten, Neue Folge, Band II (Verlag von J. A. Stargardt, Marburg, Germany, 1984) Tafel 75
- Gwenno Piette, A concise History of Brittany (University of Wales Press, Cardiff, 2008), p. 38
- The Gesta Normannorum Ducum of William of Jumieges, Orderic Vitalis, and Robert of Torigni, Vol. II, Ed. & Trans. Elisabeth M. C. Van Houts (The Clarendon Press, Oxford, New York, UK, 1995), pp. 14–5
- Francois Neveux, A Brief History of the Normans, Trans. Howard Curtis (Constable & Robinson, Ltd., London, 2006), p. 108
- David C. Douglas, William the Conqueror (University of California Press, Berkeley and Los Angeles, 1964), pp. 32–3
- David Crouch, The Normans (Hambledon Continuum, New York, 2007), p. 50
- The Gesta Normannorum Ducum of William of Jumieges, Orderic Vitalis, and Robert of Torigni, Vol. II, Ed. & Trans. Elisabeth M. C. Van Houts (The Clarendon Press, Oxford, New York, UK, 1995), pp. 78–9
- Ordericus Vitalis, The Ecclesiastical History of England and Normandy, Trans. Thomas Forester, Volume II (Henry G. Bohn, London, 1854), p. 161
- Richard E. Barton, Lordship in the County of Maine, c. 890–1160 (The Boydell Press, Woodbridge, 2004). pp. 47, 87
- David Crouch, The Normans (Hambledon Continuum, New York, 2007), p. 61.
- Ordericus Vitalis, The Ecclesiastical History of England and Normandy, Trans. Thomas Forester, Volume II (Henry G. Bohn, London, 1854), p. 74