Question: Æthelstan Half-King left his position and became a monk after the death of a king who ruled England starting which year ?

Context articles: Israel the Grammarian
Æthelstan Half-King
Æthelfrith of Mercia
Olaf Guthfrithson
Royal Arms of England
Alston (name)
Ælfhere, Ealdorman of Mercia
Thomas Jenkins (headmaster)
Eadred
Eadric, Ealdorman of Wessex

Israel the Grammarian (  895 – c. 965) was one of the leading European scholars of the mid-tenth century.
 In the 930s, he was at the court of King Æthelstan of England (r. 924–39).
 After Æthelstan's death, Israel successfully sought the patronage of Archbishop Rotbert of Trier and became tutor to Bruno, later the Archbishop of Cologne.
 In the late 940s Israel is recorded as a bishop, and at the end of his life he was a monk at the Benedictine monastery of Saint-Maximin in Trier.
Æthelstan (fl.
 932 - 956), was an important and influential Ealdorman of East Anglia who interacted with five kings of England, including his adopted son Edgar the Peaceful.
 Many of Æthelstan's close relatives were also involved in important affairs, but soon after the death of king Eadred in 955, he left his position and became a monk at Glastonbury Abbey.
Æthelfrith (fl.
 880s – c. 904/915) was an ealdorman of southern Mercia, who flourished in the last two decades of the ninth century and the first decade of the tenth century.
 His father is unknown.
 He was married to Æthelgyth, daughter of Æthelwulf; Æthelwulf is unidentified, but a possible candidate is King Alfred the Great's brother-in-law, the ealdorman of the Gaini who died in 901.
 Æthelfrith was father to four ealdormen: Æthelstan Half-King (East Anglia), Ælfstan (Mercia), Æthelwald (Kent), and Eadric (Hampshire).
Olaf Guthfrithson (Old Norse: "Óláfr Guðrøðsson" ; ; Old Irish: "Amlaíb mac Gofraid" ; died 941) was a Viking leader who ruled Dublin and Viking Northumbria in the 10th century.
 He was the son of Gofraid ua Ímair and great-grandson of Ímar, making him one of the Uí Ímair.
 Olaf succeeded his father as King of Dublin in 934 and succeeded in establishing dominance over the Vikings of Limerick when he captured their king, Amlaíb Cenncairech, in 937.
 That same year he allied with Constantine II of Scotland in an attempt to reclaim the Kingdom of Northumbria which his father had ruled briefly in 927.
 The forces of Olaf and Constantine were defeated by the English led by Æthelstan at the Battle of Brunanburh.
The Royal Arms of England are the armorials (or coat of arms) first adopted in a fixed form at the start of the age of heraldry (circa 1200) as personal arms by the Plantagenet kings who ruled England from 1154.
 In the popular mind they have come to symbolise the nation of England, although according to heraldic usage nations do not bear arms, only persons and corporations do.
 The blazon of the Arms of Plantagenet is: "Gules, three lions passant guardant in pale or armed and langued azure", signifying three identical gold lions (also known as leopards) with blue tongues and claws, walking past but facing the observer, arranged in a column on a red background.
 Although the tincture "azure" of tongue and claws is not cited in many blazons, they are historically a distinguishing feature of the Arms of England.
 This coat, designed in the High Middle Ages, has been variously combined with those of the Kings of France, Scotland, a symbol of Ireland, the House of Nassau and the Kingdom of Hanover, according to dynastic and other political changes occurring in England, but has not altered since it took a fixed form in the reign of Richard I (1189–1199), the second Plantagenet king.
Alston is an English language surname of Anglo-Saxon origin with several derivations.
 It may have evolved from the Middle English given name "Alstan", the prefix, "Al-" itself derived from different Old English words ("noble", "elf", "old", "shrine", "temple"), and the suffix "-stan" ("stone") derived from pre 7th century Old English.
 The oldest public record of this derivation is found in 1279 in Cambridgeshire.
 One branch of this name may have been taken from the manor of a Saxon Lord called Alstanus, he had his manor in Stambourne, North East Essex.
 It is known that he was still in possession of the Manor after the Norman conquest, although as a tenant rather than owner, he held the land annexed against the King.
 There are a high density of families with the surname Alston and Alliston from around the Sudbury area, not far from Stambourne.
 In the 1224 feet of fines it is recorded that John son of Adam de Alliston sold land at Stanfeld (Stansfield) Suffolk.
 Stansfield is a few miles North of Stambourne.
 Both Stambourne and Stansfield may have taken their name from Æthelstan Half-King, Earl of East Anglia in the 930s.
Ælfhere (died in 983) was ealdorman of Mercia.
 His family, along with those of Æthelstan Half-King and Æthelstan Rota, rose to greatness in the middle third of the 10th century.
 In the reign of Edward the Martyr, Ælfhere was a leader of the anti-monastic reaction and an ally of Edward's stepmother Queen Dowager Ælfthryth.
 After the killing of Edward by Ælfthryth's servants in 978, Ælfhere supported the new king, Ælfthryth's son Æthelred the Unready, and was the leading nobleman in the Kingdom of England until his death in 983.
Thomas Jenkins was the headmaster of the King Edward VI Grammar School in Stratford-upon-Avon in England starting in 1575.
 As such, his claim to fame is that William Shakespeare is considered likely to have been one of his students.
 No school records from the period survive; however, Jenkins is believed to have been of Welsh extraction, and a Welsh schoolmaster Sir Hugh Evans features in Shakespeare's play "The Merry Wives of Windsor".
 Jenkins would have taught Shakespeare Latin grammar and literature.
 It has been speculated that Jenkins taught, and awakened in Shakespeare, an interest in the legendary history of the British Isles, and as such influenced Shakespeare to create plays featuring this material, such as "King Lear" and "Cymbeline".
Eadred (also Edred) (923 – 23 November 955) was King of the English from 946 until his death.
 He was the son of Edward the Elder and his third wife Eadgifu of Kent, and a grandson of Alfred the Great.
 Eadred came to the throne following the assassination of his older brother, Edmund I.
 The chief achievement of his reign was to bring the Kingdom of Northumbria under total English control, which occurred with the defeat and expulsion of Eric Bloodaxe in 954.
 Eadred died at the age of 32 having never married, and was succeeded by his 15-year-old nephew, Eadwig.
Eadric (fl.
 942–949) was a tenth-century ealdorman of Wessex.
 He was the youngest of four sons of Æthelfrith, an ealdorman in Mercia, and his wife Æthelgyth.
 From 946 until his death in 949 Eadric was the second most senior ealdorman in England, surpassed only by his brother Æthelstan Half-King.