Question: What day did the son of Lady Margaret Beufort seize the English crown?

Context paragraphs:
John Estrete: John Estrete, or Strete (died c.1491) was an Irish judge and statesman of the late fifteenth century.  He held the offices of King's Serjeant, Deputy Chief Baron of the Irish Exchequer, and Master of the Coinage of Ireland.  He was a member of the Privy Council of Ireland.  He was a supporter of Gerald FitzGerald, 8th Earl of Kildare, who was almost all-powerful in Ireland for many years, and was prepared to defy the English Crown on occasion.  Despite his close FitzGerald connection Estrete in time gained the confidence of the English Crown, and acted as an intermediary between the Crown and Kildare, notably during the rebellion of Lambert Simnel.

Earl of Richmond: The now-extinct title of Earl of Richmond was created many times in the Peerage of England.  The earldom of Richmond was initially held by various Breton nobles associated with the Ducal crown of Brittany; sometimes the holder was the Breton Duke himself, including one member of the cadet branch of the French Capetian dynasty.  The historical ties between the Ducal crown of Brittany and this English Earldom were maintained ceremonially by the Breton dukes even after England ceased to recognize the Breton Dukes as Earls of England and those dukes rendered homage to the King of France, rather than the English crown.  It was then held either by members of the English royal families of Plantagenet and Tudor, or English nobles closely associated with the English crown.  It was eventually merged into the English crown during the reign of Henry VII and has been recreated as a Dukedom.

List of Principals of Lady Margaret Hall, Oxford: A list of Principals of Lady Margaret Hall, Oxford.  The head of Lady Margaret Hall, University of Oxford is called the Principal.  The current Principal is the former newspaper editor Alan Rusbridger, since 2015.

Lady Margaret Boat Club: The Lady Margaret Boat Club (abbreviated to "LMBC" and known as "Maggie") is the rowing club for members of St John's College, Cambridge, England.  The club is named after Lady Margaret Beaufort, founder of the College.  The Lady Margaret men's first boat is currently Head of the River for both Lent Bumps (Lent Bumps 2017) and May Bumps (May Bumps 2016).  They are current winners of the Oxford/Cambridge Men's Intercollegiate fixture at the Henley Boat Races, beating Oriel College, Oxford with a verdict of 4 lengths.

Hugh Oldham: Hugh Oldham (c.1452 – 25 June 1519) was a Bishop of Exeter and a notable patron of education.  Born in Lancashire to a family of minor gentry, he probably attended both Oxford and Cambridge universities, following which he was a clerk at Durham, then a rector in Cornwall before being employed by Lady Margaret Beaufort (mother of King Henry VII), rising to be the chancellor of her household by 1503.  During this time he was preferred with many religious posts all over the country, being made archdeacon of Exeter in 1502 and finally bishop of that city in 1505, a decision that was probably influenced by Lady Margaret.

Lady Margaret Hall Boat Club: Lady Margaret Hall Boat Club (LMHBC) is a rowing club for members and staff of Lady Margaret Hall (LMH), Oxford.

Lady Margaret's Professor of Divinity (Cambridge): The Lady Margaret's Professor of Divinity is the oldest professorship at the University of Cambridge.  It was founded initially as a readership by Lady Margaret Beaufort, mother of Henry VII, in 1502.

Henry VII of England: Henry VII (Welsh: "Harri Tudur" ; 28 January 1457 – 21 April 1509) was King of England from seizing the crown on 22 August 1485 until his death on 21 April 1509, and the first monarch of the House of Tudor.  He ruled the Principality of Wales until 29 November 1489 and was Lord of Ireland.

Ruaidhrí Mac Ruaidhrí: Ruaidhrí Mac Ruaidhrí (died 14 October 1318?)  was a fourteenth-century Scottish magnate and chief of Clann Ruaidhrí.  He was an illegitimate son of Ailéan mac Ruaidhrí, and is recorded to have participated in the kindred's military actions against supporters of both the English Crown and Scottish Crown.  Following the apparent death of his brother, Lachlann, Ruaidhrí appears to have taken control of the kindred, and firmly aligned the family with Robert I, King of Scotland.  Ruaidhrí may well be the member of Clann Ruaidhrí who is recorded slain at the Battle of Faughart in support of the Bruce cause in Ireland.  After his death, Ruaidhrí's half-sister, Cairistíona, attempted to transfer the Clann Ruaidhrí territories outwith the family.  Ruaidhrí was survived by a daughter, Áine, and an illegitimate son, Raghnall.  The latter fended off Cairistíona's actions and succeeded to the chiefship of Clann Ruaidhrí.

Carol Harrison (theologian): Carol Harrison is a British theologian, church historian and academic, specialising in Augustine of Hippo.  Since January 2015, she has been Lady Margaret Professor of Divinity at the University of Oxford; she is the first woman and first lay person to hold this appointment.  She is a fellow of Christ Church, Oxford and an honorary fellow of Lady Margaret Hall, Oxford.  On 27 April 2015, she was installed as a Canon of Christ Church Cathedral, Oxford.  She was previously Professor of the History and Theology of the Latin West at Durham University.

Supporting paragraphs: Lady Margaret's Professor of Divinity (Cambridge) Henry VII of England
Answer: 22 August 1485