POD: Joan of England survives/doesn't contract the Black Death in 1348 and makes it to her marriage to Pedro of Castile. Pretty significant butterflies ensue. Thanks to
@CaptainShadow for the suggestions so far.
Edward III, King of England (b. 1312, d. ?) m. Philippa of Hainault (b. c. 1310-1315, d. ?) in 1328, had issue
1) Edward IV, King of England (b. 1330, d. ?) m. Eleanor of Portugal (b. 1328, d. 1358) in 1351, had issue (a); Joan, 4th countess of Kent (b. 1326/1327, d. ?) in 1361, had issue (b)
1a) Philippa of England (b. 1353, d. ?)
2a) Beatrice of England (b. 1354, d. ?)
3a) Edward of Windsor (b. and d. 1356)
4a) Eleanor of England (b. and d. 1357)
5b) Edward V, King of England (b. 1365, d. ?)
6b) Richard of Bordeaux, Duke of York (b. 1367, d. ?)
2) Isabella of England, Duchess of Brabant (b. 1332, d. ?) m. Henry V, Duke of Brabant (B. ?, d. ?) in 1356, had issue
1) John IV, Duke of Brabant (b. 1357, d. ?) m. Joan of France (b. 1351, d. ?)
2) Marie of Brabant (b. 1358, d. ?)
3) Philippa of Brabant (b. 1360, d. ?)
4) Henry of Brabant (b. 1361, d. ?)
5) Joanna of Brabant (b. 1363, d. ?)
6) Eduard of Brabant (b. 1366, d. 1367)
7) Isabella of Brabant (b. 1367, d. 1372)
3) Joan of England, Queen of Castile (b. 1333/1334, d. ?) m. Pedro I, King of Castile (b. 1334, d. ?) in 1348, had issue
1) Constanza of Castile (b. 1351, d. ?) m. John I, King of Aragon (b. 1350)
2) Beatriz of Castile (b. 1352, d. ?) m. Nuño Díaz de Haro, Lord of Lara and Biscay (b. 1348)
3) Alfonso XII, King of Castile (b. 1354, d. ?) m. Eleanor of Aragon (b. 1358)
4) Isabel of Castile (b. 1356, d. ?) m. Secondotto Paleologus, Marquess of Montferrat (b. 1358, d. ?)
5) Fernando of Castile (b. 1358, d. 1359)
6) Maria of Castile (b. 1361, d. ?) m. Charles III, King of Navarre (b. 1361)
4) William of Hatfield (b. and d. 1336)
5) Lionel of Antwerp, Duke of Clarence (b. 1338, d. ?) m. Elizabeth de Burgh, 4th Countess of Ulster (b. 1332, d. ?) in 1352, had issue
1) Edward of Eltham, 2nd Duke of Clarence (b. 1355, d. ?)
6) John of Gaunt, Duke of Lancaster (b. 1340, d. 1364) m. Blanche of Lancaster (b. 1342, d. ?) in 1359, had issue
1) Philippa of Lancaster (b. and d. 1360)
2) Henry of Kenilworth, 2nd Duke of Lancaster (b. 1362, d. ?)
3) John of Burford, Duke of Hereford (b. 1363, d. ?)
4) Edward (b. and d. 1365)
7) Edmund of Langley, Duke of Cambridge (b. 1341, d. ?) m. Caterina Visconti (b. 1342, d. ?) in 1358, had issue
1) Edoardo Plantagenet, Lord of Lodi, Parma, Piacenza, and Bologna (b. 1360, d. ?)
8) Blanche of England (b. and d. 1342)
9) Mary of Waltham, Duchess of Brittany (b. 1344, d. 1366) m. John IV, Duke of Brittany
1) John (b. and d. 1364)
2) Marie of Brittany (b. 1366, d. ?)
10) Margaret of Windsor (b. 1346, d. 1348)
11) Thomas (b. 1347, d. 1348)
12) William of Windsor, Count of Armagnac (b. 1348, d. ?) m. Joan I, Countess of Armagnac (b. 1346, d. ?) in 1362, had issue
1) William II, Count of Armagnac (b. 1364, d. 1382)
2) Joan II, Countess of Armagnac (b. 1366, d. ?)
3) Beatrice of Armagnac (b. 1367, d. ?)
4) John (b. 1370, d. 1374)
13) Thomas of Woodstock, Archbishop of Rouen (b. 1355, d. ?)
- insert probable illegitimate issue here