Sources

1) Source: Chancery: Inquisitions Post Mortem, Series I, Henry VI "Norfolk, Elizabeth [Fitzalan], who was the wife of Thomas [Mowbray], Duke of, and daughter of Richard [Fitzalan], Earl of Arundel: Cambs, Oxon, Wilts, Glos, Calais, Beds, Bucks, Salop, Essex, Kent, Heref, Northants, Derb, Yorks, Warw, Leics, Surrey, Sussex, Lincs""She died on 8 July last. John duke of Norfolk is her son and next heir and the son and heir of Thomas, late duke of Norfolk , and is aged 30 years and more.""She held the manor of Prittlewell jointly enfeoffed with Thomas late duke of Norfolk , her former husband, by grant of Richard late earl of Arundel , her father, to Thomas and Elizabeth and the heirs of their bodies. "Dated: 13 Jul 1425. External Link
http://discovery.nationalarchives.gov.uk/details/r/C6158709. Reference: C 139/16/25. King's College London, 2014. | Mapping the Medieval Countryside [online]. Available at http://www.inquisitionspostmortem.ac.uk/view/inquisition/22-418/423 (Data from secondary evidence)
2) Source: The Berkeley Estate "Philip Mede, burgess of Bristol, and Richard his son and heir; and Maurice Berkeley, esquire, son of James late lord Berkeley, and Isabel his wife. Mon. after All Saints, 14 Edw. IV". Dated: 7 November 1474.. External Link
https://discovery.nationalarchives.gov.uk/details/r/48197816-d81d-4b9d-aa1d-e46d288722f9. Reference: BCM/A/2/43/16 (Data from direct source)
3) Source: The Mowbray Estate "John duke of Norfolk, son and heir of John late duke; and his beloved cousin William Berkeley, lord of Berkeley, knight, and Joan his wife. 4 June 15 Edw. IV". Dated: 1475.. External Link
https://discovery.nationalarchives.gov.uk/details/r/1c8357fd-7064-4323-9363-c9aff0a236d1. Reference: BCM/D/1/1/18 (Questionable reliability of evidence)