Here is one of 12 descents of Elizabeth Willoughby from Matilda of Perche, bastard daughter of King Henry I of England:
(This Matilda holds a very tragic place in English history. In 1120 the "Blanch
Nef" carrying William Atheling, only legitimate son and heir of King Henry,
foundered off the coast of Barfleur, France. The Prince was hastened aboard
a rowboat and was being taken safely to shore, but hearing the cries for
help from his half-sister Matilda who remained on board the sinking ship,
he insisted on returning to try and rescue her. As they neared the ship,
so many drowning people attempted to climb aboard the small craft carrying
the Prince that it too was sunk, leaving the king without a male heir to
the throne, and setting the stage for the later conflict between Henry's
only surviving legitimate daughter "Matilda Empress" and her cousin Stephen
of Blois. This conflict plunged England into a bloody Civil War with all
the leading Barons taking sides, and for years all semblance of law and order
ceased in the Kingdom).
This line is no longer valid. See generation #16 below for the break in the line:
1. Elizabeth Willoughby 1512-1562 = Sir Fulke Grevill, knight
2. Edward Willoughby ca. 1491-1517 = Margaret Nevill
3. Robert Willoughby, Lord Broke 1470-1521 = Elizabeth Beauchamp
4. Robert Willoughby, Lord Broke = Blanche Champernoun 1452-1480
5. Sir John Champernoun = Elizabeth Bigbury 1426-1469/74
6. Sir William Bykeberry bef. 1380-1426 = Elizabeth Powlett
6. Sir William Bykeberry = Katherine Stonehouse d. aft. 1390
7. Thomas Stonehouse = unknown
8. Thomas Stonehouse = Margaret Champernoun
9. Oliver Champernoun = Eglina de Valletort
10. Sir Richard Champernoun = Joan de Okeston d. bef. 1319
11. Richard, Earl of Cornwall 1209-1272 = Joan (his mistress)
12. John Lackland, King of England = Isabella of Angouleme 1188-1246
14. Aymer "Taillfer" de Valence, Count of Angouleme d. 1218 = Alice de Courtenay
15. William IV, Count of Angouleme = Marguerite de Turenne
16. Raymond I, Vicomte de Turenne = Maud de Perche d. 1143
Maud de Perche, formerly considered to be the daughter of Routrou II, is now believed to be his sister, based on chronology. So the line breaks at this point.
17. Routrou II, Count de Perche = Matilda 1086-1120
18. Henry Beauclerc, King of England 1068-1135 = Edith, a mistress