A post about Edward II's kinswoman, Isabel of Castile, queen of Aragon and duchess of Brittany (1283-1328), who, in different circumstances, might have been his queen.
Infanta Doña Isabel was born in Toro between Zamora and Valladolid in northern Spain sometime in 1283 as the granddaughter of the then reigning king of Castile, Alfonso X (Eleanor of Castile's half-brother and thus Edward II's uncle). Her mother was Maria de Molina, who was born in the late 1250s or early 1260s and was the daughter of Fernando III's brother Alfonso, lord of Molina, and her father was Sancho, second son of Alfonso X and grandson of Fernando III, born in May 1258 (Isabel's parents were first cousins once removed). Isabel was the eldest of the children of Sancho and Maria, who had married in Toledo in July 1282, and her younger siblings were: King Fernando IV, December 1285 - September 1312; Pedro, lord of Los Cameros, born 1290, killed at the battle of Vega de Grenada in 1319; Felipe, lord of Cabrera and Ribera, May 1292 - April 1327; Beatriz, queen of Portugal, 1293 - October 1359; and two brothers, Alfonso and Enrique, who died in childhood. Her father also had three known illegitimate children. Isabel was Edward II's first cousin once removed on her father's side and his second cousin on her mother's. She was also the second cousin of Edward's queen Isabella of France, both of them great-granddaughters of King Jaime I 'el Conquistador' of Aragon and his queen, Yolande of Hungary; Jaime and Yolande's daughter Violante was queen of Castile, their daughter Isabel queen of France.
When Isabel was a few months old, in April 1284, her grandfather Alfonso X died, and her father seized the throne of Castile as Sancho IV, ignoring the claims of his young nephews, the sons of his dead older brother Fernando de la Cerda ('of the bristle'). Alfonso X cursed Sancho on his deathbed for this disinheritance of his grandsons.  Apparently Isabel was betrothed as a child to her first cousin, Fernando de la Cerda's elder son Alfonso, whose mother Blanche was the daughter of Louis IX of France, though ultimately nothing came of it. What Isabel's childhood and relationship with her parents were like is a matter for speculation, though her father Sancho is known to have beaten men, dissident nobles, to death with his own hands, which gives some insight into the kind of court she grew up in.  She married very young: in Soria (between Valladolid and Zaragoza) in December 1291, when she was just eight years old, she was married to King Jaime II of Aragon, as a means of securing peace between Aragon and Castile. Jaime was then twenty-four and had succeeded his childless brother Alfonso III, who had long been betrothed to the future Edward II's eldest sister Eleanor, the previous June.
Sancho IV died on 25 April 1295, not yet thirty-seven, leaving Isabel, then eleven or twelve, his eldest son Fernando IV, aged nine, as his successor, and four younger children. Shortly before his death, Sancho appointed his wife Queen Maria as guardian of their eldest son and as regent of Castile during the boy's minority.  Castile erupted into chaos and civil war on the accession of the boy-king Fernando; his father had wrongfully seized the throne and his de la Cerda cousins, backed by France, had a strong claim; Sancho IV's brother Infante Don Juan also claimed the throne; the marriage of Sancho and Maria de Molina was said to have been uncanonical - presumably they hadn't received a dispensation for consanguinity - and their children thus illegitimate. The strenuous efforts of the powerful, intelligent and politically astute Queen Maria saved the throne for her son Fernando, and in 1301 her and Sancho's marriage was declared to have been legal, which also calmed the situation considerably.  Her eldest child Isabel, the young queen of Aragon, was not so lucky, however. Jaime II had their unconsummated marriage annulled on the grounds of consanguinity* soon after her father's death, presumably because the turmoil in Castile made the kingdom an unattractive ally and because he hoped to use the chaos to his own advantage. He married instead, on 29 October or 1 November 1295, Blanche of Anjou, the second daughter of Charles of Salerno, king of Naples and Albania (Blanche's brothers were king of Hungary, king of Jerusalem, titular emperor of Constantinople and so on). Blanche was the mother of Jaime's successor Alfonso IV.
* Isabel and Jaime were first cousins once removed: Isabel was the great-granddaughter, via Alfonso X's queen Violante, of Jaime I 'el Conquistador' of Aragon, Jaime his grandson. They were related in the same way that her parents were. The marriage of Fernando III's parents Alfonso IX of Leon and Berenguela of Castile was also annulled by the pope in the early 1200s on the grounds that they were first cousins once removed. You'd think the Iberian kings would have figured out that they needed a papal dispensation to marry relatives.
Isabel, still only twelve, presumably returned to Castile and lived at her brother Fernando IV's court for the next few years; she was not to marry again until she was twenty-seven. In January 1302 in Valladolid, she probably attended her sixteen-year-old brother's wedding to Constança of Portugal - Constança was their first cousin once removed, as her grandmother Beatriz, queen of Portugal, was an illegitimate daughter of Alfonso X of Castile and thus Sancho IV's half-sister. Constança was also Jaime II of Aragon's niece. Isabel's sister Beatriz, ten years her junior, married Constança's brother the future King Afonso IV of Portugal in September 1309, and in 1310 her brother Pedro married Maria, one of the daughters of Isabel's former husband Jaime II by his second wife Blanche of Anjou. How Isabel felt about that is not recorded. (The Iberian kings of the era were extremely inter-related; Fernando IV and Constança's son Alfonso XI married Maria of Portugal, daughter of Beatriz of Castile and Afonso IV, who was his first cousin on both sides of the family.)
In 1303, Edward of Caernarfon's colourful uncle Infante Don Enrique, who was Isabel's great-uncle - he was one of the brothers of Alfonso X - proposed Isabel as a bride for the future king of England. The two were close in age, Isabel just a few months older, and it may be the half-Castilian Edward would have liked to marry a woman from that country, but his betrothal to Philip IV of France's daughter Isabella, arranged in 1299, could not be broken without England losing Gascony and going to war with France. Edward I wrote courteously to Enrique, whom he had probably known very well in the 1250s when Enrique rebelled against his brother Alfonso X and lived in exile at Henry III's court in England for several years, on 10 April 1303, thanking him for "using his influence in the matter of a marriage between Edward, the king's son, and Infanta Isabel, daughter of the late King Sancho, king of Castile and Leon, Henry [Enrique]'s cousins. The king requests him to give credence to what Gunsalvius Martini, Henry's man and the bringer of his letters, who is carrying the present letters, shall explain to him by word of mouth, as the king has fully opened his mind to him in the things that concern the matter aforesaid."  I wonder what Edward said, and what he and his son felt about this possible match with the younger Edward's first cousin once removed.
Isabel finally married again when she was twenty-seven in 1310, apparently in Burgos: her husband was the future Duke John III 'the Good' of Brittany, who was two and a half or three years her junior, born on 8 March 1286. John was, in what appears to be a major feature of this blog post, also a first cousin once removed of Edward II: his father Arthur II, duke of Brittany (born 2 July 1262) was the eldest son of Edward I's sister Beatrice. John's mother was Marie of Limoges, daughter and heir of Guy, vicomte of Limoges and Marguerite, daughter of Duke Hugues IV of Burgundy. John had firstly been married, in 1298, to Isabelle, eldest child of Philip IV of France's brother Charles de Valois; her nearest sibling became Philip VI of France in 1328; the next eldest sister Jeanne was the mother of Edward III's queen Philippa of Hainault. Isabelle de Valois died in 1309, still only about seventeen, and left no children. Duke John and Doña Isabel were fourth cousins via common descent from Henry II and Eleanor of Aquitaine; Pope Clement V issued a dispensation for them to marry on 21 June 1310.  (After her own experience and that of her parents, it's hardly surprising that Isabel wanted everything to be water-tight this time.)
Isabel became duchess of Brittany and viscountess of Limoges on 27 August 1312 when her father-in-law Duke Arthur died. Her brother King Fernando IV of Castile died eleven days later at the age of only twenty-six, leaving his one-year-old son Alfonso XI as king and throwing Castile into turmoil yet again, and yet again, Isabel's astute mother Maria saved the situation for her grandson the baby king. Queen Maria, incidentally, wrote her will on 29 June 1321, and it mentions la Infanta Doña Isabel mi fija (my daughter). There's very little I can say about John and Isabel's marriage, unfortunately, or their lives in general. Pope John XXII absolved Isabel on 6 July 1317 of her vow to visit Santiago de Compostela.  Edward II was in occasional contact with his kinsman Duke John, mostly in connection with English sailors robbed or arrested within John's territory. Duke John's uncle John of Brittany, whose heir he was, was earl of Richmond and spent his life in England, loyal to Edward II until he joined Isabella and Roger Mortimer in Paris in early 1326. Roy Martin Haines has pointed out  that Edward in and after 1324 was keen to stay on good terms with Duke John as a counterbalance to the French, with whom he was then at war. Several letters and writs of Edward's from 1320 to 1325 refer to a truce and an accord of peace between the king and the duke, and one of Edward's letters to Charles IV of France regarding the non-return of Queen Isabella in late 1325 was also sent to John. Finally, Edward II wrote to John on 6 October 1324 after the outbreak of hostilities in France, as he did to his kinsmen in Castile, complaining that "Charles [IV of France] is moved against the king, God knows why..." and asking John to use his influence with Charles on Edward's behalf. 
Infanta Doña Isabel of Castile, queen of Aragon and duchess of Brittany, died on 24 July 1328, in her mid-forties, and was buried at Notre-Dame de Prières, a Cistercian abbey in Nantes which had been founded in 1252 by her husband's great-grandfather Duke John I. She left no children. Her will still exists, in the National Archives in London (I don't know how it ended up there); I have a copy of it, but sadly it's so faded it's basically illegible, and I'm really not sure if I can glean anything from it. Duchess Isabel's tomb was destroyed in the early eighteenth century when work began on a new church at Notre-Dame de Prières, although her remains were removed to another sarcophagus in the new church. This was discovered in the ruins of the abbey in 1841, and was placed in a chapel built on the site.
Duke John III married thirdly, on 21 March 1329 (or 1330 - I've seen both dates), Jeanne of Savoy (born 1310), daughter of Édouard I, count of Savoy and Blanche of Burgundy, granddaughter of Louis IX of France. Two of Blanche's sisters, Marguerite and Jeanne, were queens of France, and another sister, Marie, married Edward II's nephew Count Édouard I of Bar. John III married three times and fathered no legitimate children, though apparently he did acknowledge an illegitimate son, named John after himself. This is somewhat odd, as it seems rather implausible that his three wives were all infertile. He died on 30 April 1341 at the age of fifty-five and was buried in Ploërmel. His childless death led to the War of the Breton Succession between his niece Jeanne of Penthièvre (b. 1319), daughter and heir of John's brother Guy who died in 1331, and John's half-brother, confusingly also called John, born in c. 1293 as the son of Duke Arthur II by his second wife Yolande de Dreux, countess of Montfort and dowager queen of Scotland (having been briefly married to Alexander III, Edward I's brother-in-law, who died in an accident in March 1286).
1) Teofilo F. Ruiz, Spain's Centuries of Crisis: 1300-1474, p. 53.
2) Malcolm Vale, 'Ritual Ceremony and the 'Civilising Process': The Role of the Court, c. 1270-1400' in Steven J. Gunn and A. Janse, eds., The Court as a Stage (2006), p, 27; Teofilo F. Ruiz, The City and the Realm 1080-1492, p. 144.
3) Evelyn S. Procter, Curia and Cortes in León and Castile 1072-1295, p. 231.
4) Ruiz, Spain's Centuries of Crisis, pp. 53-55.
5) Calendar of Close Rolls 1301-1307, p. 83; Foedera 1272-1307, p. 951.
6) Foedera 1307-1327, p. 109.
7) Foedera 1307-1327, p. 336.
8) Roy Martin Haines, King Edward II: His Life, His Reign and Its Aftermath, 1284-1330, p. 175.
9) Close Rolls 1323-1327, pp. 321-322.