This is one that I've had in the back of my mind for ages, but I'll almost certainly never write another Caroline War timeline, so here goes.
POD: 1364-5
John of Montfort dies sometime after the Battle of Auray, but before signing the Treaty of Guérande. His cause of death is unimportant, but not nefarious. (He catches a fever or the plague.) The Montfortists have thus won the War of the Breton Succession, but lost their duke before the peace can be settled. The Blois-Penthièvre are similarly duke-less, with Charles of Blois dead on the field of battle and his eldest son and heir, John of Blois, a prisoner in England. John of Montfort's heir is his sister, Joan of Montfort. A plan to have John of Blois and Joan of Montfort unite their claims via marriage is quickly shot down by King Edward III, who refuses to ransom John of Blois.
Joan of Montfort, having been raised in England and being entirely dependent on the English crown, weds Edward III's fourth son, Edmund of Langley. John of Gaunt resigns the earldom of Richmond, which is restored to Joan -- and Edmund,
jure uxoris -- and the pair pick up the fight for Brittany where John would-have-been-IV left off.
Edmund of Langley wed Joan of Montfort,
suo jure duchess of Brittany and
suo jure countess of Richmond, in 1365, had issue:
- Edward I, duke of Brittany (1370-1422) wed Joan of Navarre, had issue
- Arthur III, duke of Brittany, (born 1387) wed Joan of France
- Joan (born 1389) wed King Henry V of England
- Philippa (born 1390) died young
- Bonne (born 1391) wed John I, count of Alençon
- Isabella (born 1393) wed Olivier, count of Penthièvre
- John, count of Montfort (born 1394)
- Marie (born 1396) wed Alain IX, viscount of Rohan
- Blanche (born 1397) wed Guy XIII, lord of Laval
- Constance (born 1399) abbess of Fontevrault
- Edward (born 1401) died young
- Charles (born 1403) wed Margaret of Orléans, suo jure countess of Vertus
- John, earl of Richmond (1372-1402) wed Joan Holland, had issue
- John (born 1396) dies young
- Joan (born 1398) a nun of the Order of Minoresses
- Mary (born 1402) born posthumously, dies young
- Joan (1377-1416) wed Thomas Holland, 1st duke of Surrey, no issue
Edward I, duke of Brittany, would be everything his father wasn't -- ambitious, shrewd, and strategic. He'd chart a new course for Brittany, wedding his eldest children to the royal lines of England and France and using the rest of his large brood to tie the duchy together after the long and destructive War of the Breton Succession (which would be even longer and more destructive in ATL). One of the greatest warriors of his day, he'd fight alongside the English and the French at different times as a knight errant, but would keep his duchy steadfastly neutral when the two powers were at war with one another. England would see a series of rebellions in the late 1390s and early 1400s. France would sink into civil war. Brittany would rise to new heights as they did. Through his daughter, Joan of Brittany, he is an ancestor to all future monarchs of England.
John, earl of Richmond, would inherit his mother's English lands. Once one of the greatest estates in all England, it was poorly managed by his weak father and his mother was an absentee countess at the best of times. John was thus reliant on the goodwill of his cousin, King Richard II. Richard showered John with gifts, despite the earl's limited abilities. John grew accustomed to a lifestyle he couldn't afford, making Richard's downfall in 1399 a personal disaster for him. Too cowardly to join the Epiphany Rising, he looked for support from his other cousin, the new King Henry IV, but he never found favor in the new regime. In 1402, he was discovered plotting to murder the new king and was executed. His estates were declared forfeit to the crown and his only surviving child was put into a nunnery. John's death and attainder strained relations with Brittany for a time, as John's brother, Edward I of Brittany, had come to power just months before John's death. Edward eventually accepted his family's loss of Richmond, counting it as part of his daughter, Joan of Brittany's, dowry in 1406, when she married the prince of Wales, who would later become King Henry V.
Joan of Brittany (daughter of Edmund of Langley -- not to be confused with her niece of the same name) wed Thomas Holland, nephew of King Richard II. This was part of a double marriage between the Bretons and the Hollands (see: John, earl of Richmond, above) to tie Richard's closest kin to Brittany in the dark final years of the War of the Breton Succession. The effort was a success, with the English finally putting Joan of Montfort on the ducal throne at great expense in the 1380s, but the marriage was a failure on a personal level. The two hated one another, leading Joan to tip off Henry IV as to her husband's role in the Epiphany Rising, which unraveled the whole conspiracy and led to Holland's execution in 1400. Joan was allowed to hold on much of her late husband's estates in dower, and happily lived out her days as a wealthy widow.
(Yes, yes I did intentionally name as many John/Joan as possible and wed them to as many Joans as possible just to keep that weird streak from the OTL War of the Breton Succession going.)
