ARTHUR I of BRITTANY

Duke of Brittany
(1187 AD - presumably 1203)

Heir to the Throne of England
Proclaimed King of Brittany

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Heir to King Richard I "The Lionheart"

Arthur Plantagenet was the postumous son and only heir of Duke Geoffrey II of Brittany, 4th Earl of Richmond, who was son of King Henry II, and King Richard's younger brother, next in line of succession.
Thus, after his father's death, Arthur was next in line to the Throne of England after Richard, as this latter had no descendance.

King Richard "the Lionheart" himself recognized Arthur as heir presumptive to the Throne of England in 1190, when he was only 3 years old 1Reference: Encyclopaedia Britannica, Arthur I.

Fixed background image: 6th membrane 1bReference: British Library, digitalized manuscript Royal MS 14 B VI, f.006r of the digitalized manuscript "roll chronicle of the genealogy of the Kings of Britain" dated c.1300, British Library (Royal MS 14 B VI, f.006v).

Depiction from the roll chronicle showing King Henry II's descendance
King Henry II's sons and daughters (extract from background caption) King Henry II, Duke of Normandy's descendance, ordered by ages. Males, left (oldest) to right by order of right to succession: 3rd: King Richard - 5th: Duke Geoffrey II of Brittany - 7th: John Lackland
Roll Chronicle of the Genealogy of the Kings of England, f.6r - dated 1300-1340
British Library - Manuscript Royal MS 14 B VI 2Reference: National British Library, digitalized Genealogical roll of the kings of England, manuscript Royal MS 14 B VI
Depiction of King Richard, roll chronicle of genealofy of Kings of Britain
King Richard I the Lionheart
(1157 - 1199)
Depiction of Count Geoffrey II of Brittany, roll chronicle of genealofy of Kings of Britain
Geoffrey II Duke of Brittany, Richard's younger brother (1158 - 1186)

Retained by the King of France

In 1196, Arthur's mother Constance Duchess of Brittany had the young Arthur proclaimed Duke of Brittany and her co-ruler as a child of nine years 3Reference: Arthur I of Brittany, Wikipedia website.

On the same year, Richard I sought the custody of Arthur, the young heir to Brittany, and when the Bretons refused, he invaded the duchy while Constance was held captive 4Everard, J. (2000). The end of Angevin Brittany, 1186-1203. In Brittany and the Angevins: Province and Empire 1158-1203 (Cambridge Studies in Medieval Life and Thought: Fourth Series, pp. 146-175). Cambridge: Cambridge University Press. doi:10.1017/CBO9780511496486.011.

As Richard marched from Normandy to Brittany to rescue Arthur, the latter was secretly carried to France to be brought up with Prince Louis. 5Wikipedia Reference: Everard, J. (2000). Genealogy of the dukes of Brittany, 1066-1203. In Brittany and the Angevins: Province and Empire 1158-1203 (p.146) (Cambridge Studies in Medieval Life and Thought: Fourth Series, p. Xv). Cambridge: Cambridge University Press. doi:10.1017/CBO9780511496486.002.

This eventually caused King Richard to disinherit Arthur in favour of John 6Reference: Arthur I of Brittany - Encyclopaedia Britannica, , the youngest of Richard's brothers, also known as John Lackland for not having inherited any lands from his father King Henry II.

Les Très Riches Heures du duc de Berry juin
Palais de la Cité, residence of the Kings of France from 6th to the 14th century 7Reference: Palais de la Cité - Wikipedia website Miniature from the illuminated manuscript Les Très Riches Heures du Duc de Berry, c.1400.
Located on the Île de la Cité in the Seine River in the centre of Paris, is a major historic building that was the residence of the Kings of France from the sixth century until the 14th century, and has been the center of the French justice system ever since, thus often referred to as the Palais de Justice 8Reference: Description of file Les Très Riches Heures du Duc de Berry: Juin - Wikipedia Commons .

Death of King Richard I

In 1199, King Richard "the Lionheart" died of gangrene aged 42. Apart from being King of England, Richard was Duke of Normandy, Aquitaine and Gascony; Count of Poitiers, Anjou, Maine, and Nantes 9Reference: King Richard I, Wikipedia.

His vast French territories, with exception of Rouen (Normandy), initially rejected John Lackland as a successor, preferring his nephew Arthur 10Wikipedia Reference: Jones, Dan (2014). The Plantagenets: The Warrior Kings and Queens Who Made England (pp. 150-152) - Penguin Books. ISBN 978-0-1431-2492-4..

Arthur also had the support from King Philip of France, who took up Arthur's cause, accepting his homage for all the continental lands that had been Richard's, including Normandy. He then used this as an excuse to take control of the towns and fortifications in those areas while keeping Arthur in Paris.

Depiction from Les Grandes chroniques de France showing Count Arthur doing homage to King Phillipe II of France - f. 361v (Philip Augustus, book 2, 18)
Arthur I of Brittany doing homage to Philip Augustus, (Royal MS 16 G VI,f.361v) description After King Richard's death, Arthur I of Brittany (to the right) is wearing a crown, and is doing homage to King Philip II of France in return for this latter's support to his claim to the English throne.
"Arthur of Brittany doing homage to Philip Augustus"
Les Grandes Chroniques de France, 1332-1350
British Library, Royal MS 16 G VI, f.361v

Two Kings, One Throne

John, was accepted as king in England and Normandy. King Philip, however, recognized Arthur's right to Brittany, Anjou, Aquitaine, and Maine 11Reference: Arthur I - Encyclopaedia Britannica., and Arthur led a force to Anjou and Maine 12Wikipedia Reference: Jones, Dan (2014). The Plantagenets: The Warrior Kings and Queens Who Made England - Penguin Books. ISBN 978-0-1431-2492-4..

Meanwhile, Constance was indefatigable as she worked on her son Arthur's behalf, negotiating with barons and offering lands and patronage in return for their continuing support. 13Reference: J.F. Andrews, Lost Heirs of the Medieval Crown, Pen & Sword Books..

It was only a year later, that Arthur got captured while trying to take control of Poitou with rebel nobles that followed him. It is assumed that he was taken to the castle of La Falaise, and no one ever heard of him again. Whether he was murdered, or died while being castrated, all are suppositions.

In the Treaty of Le Goulet, that John was recognized as successor in all Richard's French possessions, in return for financial and territorial concessions to Philip.

Capture from the manuscript Les Chroniques de France, mentions Arthur as King of Brittany (Royal MS 16 G VI,f.361v) lines 10-11
Arthur I of Brittany is named King Arthur of Brittany - Les Grandes Chroniques de France, c.1300 Caption of illuminated manuscript naming Duke Arthur I of Brittany as King Arthur of Brittany, and explains how he disputed the English throne to John Lackland after Richard's death:
"... Arthus li Rois de bretaigne..." (Arthur King of Brittany)
Les Grandes Chroniques de France manuscript, f. 361v (lines 10-11) - dated 1332-1350 (Philip Augustus, book 2, 18) - British Library (Royal MS 16 G VI,f.361v)