The line comes from an article in the NEHGR, however, it is not completely accepted.
- New England Historical and Genealogical Register, vol. no. 1 (January 2007): pages 27-36. “A Probable Royal Descent for Thomas Bradbury of Salisbury, Massachusetts,” by Marshall Kirk. AmericanAncestors.org link.
One line would be:
1. Robert de Ros m. Isabel of Scotland
2. Sir William de Ros m. Lucy Fitz Piers
3. Sir William de Ros m. Eustache Fitz Ralph
4. Ivetta de Ros m. Sir Geoffrey le Scrope
5. Sir Stephen le Scrope m Isabel (---)
6. Joan le Scrope m. William Pert
7. Isabel Pert m. Robert Conyers
8. Joan Conyers m. Sir Philip Dymoke
9. Sir Thomas Dymoke m. Margaret de Welles
10. Joan Dymoke m. John Fulnetby
11. Katherine Fulnetby m. William Dynewell
12. Anne Dynewell m. Henry Whitgift
13. William Whitgift m. Margaret Bell
14. Elizabeth Whitfigt m. Wymond Bradbury
15. Thomas Bradbury
The key generations in doubt would be #11 and 12.