Sources

1) Source: Exchequer: Treasury of Receipt: Ancient Deeds, Series A "Grant by Robert de Ver, Earl of Oxford, to William de Warenne, eldest son of John, Earl Warenne, and to Joan, Earl Robert's eldest daughter, of the manor of Medmenham and land in Cestresham, and to the heirs of the said William by her, with remainders."Dated: 30 Sep 1284. External Link
http://discovery.nationalarchives.gov.uk/details/r/C4938766. Reference: E 40/13 (Data from direct source)
2) Source: Chancery: Inquisitions Post Mortem, Series I, Edward I 15 December 1286:"Sir Robert de Veer, earl of Oxford, father of the said Joan... who still survivesJohn his son...is his next heir...held of Sir John earl of Warrenn' for life, with reversion to the said earl his father". External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol2/pp377-383. Reference: C 133/47/13, William de Warrenna: Oxfordshire, Norfolk, Buckinghamshire, Essex, Cheshire, Flintshire (Data from secondary evidence)
3) Source: Special Collections: Ancient Petitions "People mentioned: Robert [de Vere], Earl of Oxford; Alice [de Vere, Countess of Oxford]; Henry III, King of England; Richard de Lovetoft, clerk; Bishop of Norwich; Edward I, King of England; William de Warenne; Joan [de Warenne], wife of William de Warenne; John de Warenne; Ivo de Audewincle; John de Warenne, son of John de Warenne; Alice [de Warenne], daughter of John de Warenne, senior, sister of John de Warenne, junior; Richard [FitzAlan], son of Alice de Warenne; Richard [FitzAlan], son of Richard FitzAlan, father of the petitioner; William Cokkyng, clerk; Richard II, King of England; Maurice Campeden; Payn Tiptot, knight; Peter Brauncher (Braunche)." Dated: c1402. External Link
https://discovery.nationalarchives.gov.uk/details/r/C9295233. Reference: SC 8/188/9355 (Data from secondary evidence)