William Aldeburgh, 1st Baron Aldeburgh 1) 2)
Died 1388 1)
Notes: William de Aldeburgh, 1st Baron Aldeburgh was a 14th-century English nobleman and the builder of Harewood Castle. Of Aldeburgh and Harewood. Co-heiress of William, 2nd Lord Aldeburgh, her brother.
Elizabeth Unknown 3)
Notes: William is traditionally said to have married Elizabeth, daughter of John de L'Isle. While there are various property transactions which suggest this could have been the case - e.g. transfer of Harewood castle - it should be noted that these were all purchases, therefore are of very limited weight. The theory can, however, be discounted (or at least made very unlikely) based on her seal, which survives and depicts her arms - these are very distinct to the de L'Isle arms.
John Mowbray and Margaret Percy, have been suggested by Libby Richardson as alternative parents - https://groups.google.com/g/soc.genealogy.medieval/c/SIIRO5QqROQ/m/umGXKOSkZukJ - but again, the evidence is weak: the seal seeming to have the Mowbray arms, and other property transactions.
1. Elizabeth Aldeburgh 1)
Born 1364 1) 2)
Died 21 Dec 1417, 52 or 53 years 1)
Notes: Elizabeth, and her sister Sibyl were heiresses to their brother William Aldeburgh, 2nd Baron Aldeburgh, when he died without issue. Their inheritance included Harewood castle, whose occupation the sisters and their families subsequently shared.
Sources1) Source: The History of Parliament . External Link
http://www.historyofparliamentonline.org/volume/1386-1421/member/stapleton-sir-brian-1417. Reference: Stapleton, Sir Brian (d.1417), of Carlton, Yorks. (Questionable reliability of evidence)
2) Source: Chancery: Inquisitions Post Mortem, Series I, Richard II "He died on 20 August last. Elizabeth late the wife of Brian de Stapilton, the younger, knight, aged 28 years and more, and Sibyl wife of William de Ryther, knight, aged 25 years and more, are his sisters and heirs. The said William de Ryther and Sibyl have issue... He held the under-mentioned manor of Kelfeld jointly with Margery his wife, deceased, by gift and grant of William de Kyrkeby, chaplain, and Robert de Tyndale to William de Aldeburgh, knight, his father, deceased, for life, with successive remainders to him and the said Margery and the heirs of their bodies, and to the right heirs of the said William de Aldeburgh, his father." Date: 1392. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol16/pp433-455. Reference: C 136/69/2 (Data from direct source)
3) Source: Chancery: Inquisitions Ad Quod Damnum, Henry III to Richard III "Robert de Insula of Rougemont, knight, to grant two-thirds of the manor of Harewood, except a messuage and land in Carlton, with the reversion of the other third, now held for life by Maud late the wife of John his father, to William de Aldeburgh, knight, Elizabeth his wife, and his heirs, retaining the said exceptions, with rent. York." Date: 1364. External Link
https://discovery.nationalarchives.gov.uk/details/r/C7575947. Reference: https://discovery.nationalarchives.gov.uk/browse/r/h/C3701 (Data from secondary evidence)