Here is a descent of Elizabeth Willoughby from William the Lion, King of Scotland, through his bastard daughter, Isabel:
1. Elizabeth Willoughby 1512-1562 = Sir Fulke Grevill, knight
2. Edward Willoughby 1491-1517 = Margaret Nevill
3. Sir Robert Willoughby, Lord Broke 1470-1521 = Elizabeth Beauchamp
4. Sir Robert Willoughby, Lord Broke 1452-1502 = Blanche Champernoun
5. Sir John Willoughby ca. 1421-1477 = Anne Cheyney
6. Sir John Willoughby ca. 1400-1346/7 = Jane Welby
7. Sir Thomas Willoughby d. 1417 = Elizabeth Neville
8. Robert Willoughby, Lord of Eresby = Margery la Zouche d. 1391
9. William la Zouche, Lord Zouche = Elizaberh de Ros d. 1380
10. William de Ros, Lord Ros d. 1342/3 = Margery de Badlesmere
11. William de Ros, Lord Ros d. 1316 = Maud de Vaux
12. Sir Robert de Ros d. 1285 = Isabel d'Aubigny
13. Sir William de Ros d. ca. 1264 = Lucy fitz Piers
14. Robert de Ros = Isabel of Scotland
15. William the Lion, King of Scotland 1143-1214 = _____ Avenel, a mistress