Question: Which king of Northumbria, who possibly became king while a still a child, attempted to have Eardwulf of Northumbria assassinated?

Passages:
The Southumbrians or 'Suðanhymbre' were the Anglo-Saxon people occupying northern Mercia.  The term might not have been used by the Mercians, and instead possibly coined by the Deiran or Bernician people as a territorial response to their own Kingdom of Northumbria.  The "Anglo-Saxon Chronicle" refers to King Coenred as having become the King of the Southumbrians in 702, two years before he became King of all the Mercians.  The fact that Coenred was the son of Wulfhere, the Mercian King, implies that Southumbria was a sub-kingdom of Mercia. Æthelred ( ; c. 762  – 18 April 796), was the king of Northumbria from 774 to 779 and again from 790 until he was murdered in 796.  He was the son of Æthelwald Moll and Æthelthryth and possibly became king while still a child after Alhred was deposed. Alkmund of Derby (or of Lilleshall), also spelt Ealhmund, Alhmund, Alcmund, or Alchmund (d. c. 800) was a son of Alhred of Northumbria.  After more than twenty years in exile as a result of Northumbrian dynastic struggles, he returned with an army.  He was killed in about 800, for which King Eardwulf of Northumbria was held responsible.  Whatever the exact circumstances, his death was regarded as a martyrdom, and Alkmund as a saint. Ælfwald, according to one tradition, reigned as king of Northumbria following the deposition of Eardwulf in 806.  This information appears only in the anonymous tract "De primo Saxonum adventu" and in the later "Flores Historiarum" of Roger of Wendover.  Roger states that Ælfwald had overthrown Eardwulf. Eanflæd (19 April 626 – after 685, also known as Enfleda) was a Deiran princess, queen of Northumbria and later, the abbess of an influential Christian monastery in Whitby, England.  She was the daughter of King Edwin of Northumbria and Æthelburg, who in turn was the daughter of King Æthelberht of Kent.  In or shortly after 642 Eanflæd became the second wife of King Oswiu of Northumbria.  After Oswiu's death in 670, she retired to Whitby Abbey, which had been founded by Hilda of Whitby.  Eanflæd became the abbess around 680 and remained there until her death.  The monastery had strong association with members of the Northumbrian royal family and played an important role in the establishment of Roman Christianity in England. Earl of Northumbria was a title in the Anglo-Danish, late Anglo-Saxon, and early Anglo-Norman period in England.  The earldom of Northumbria was the successor of the earldom of Bamburgh.  In the seventh century, the Anglo-Saxon kingdoms of Bernicia and Deira were united in the kingdom of Northumbria, but this was destroyed by the Vikings in 867.  Southern Northumbria, the former Deira, then became the Viking kingdom of York, while English earls ruled the former northern kingdom of Bernicia from their base at Bamburgh.  The northern part of Bernicia was lost to the Scots, probably in the late tenth century.  In 1006 Uhtred the Bold was earl of Bamburgh, and Æthelred the Unready appointed him earl of York as well, re-uniting the area of Northumbria still under English control into a single earldom.  Uhtred was murdered in 1016, and Cnut then appointed Eric of Hlathir earl of Northumbria at York, but Uhtred's dynasty held onto Bernicia until 1041, when the earldom was again united.  A descendant of Uhtred, Gospatric, was appointed earl by William the Conqueror in 1067, but William expelled him in 1072.  Gospatric was then given lands in Scotland, and his descendants became earls of Dunbar.  The earldom of Northumbria was broken up in the early Norman period and dissolved into the earldoms of York and Northumberland, with much land going to the prince-bishopric of Durham. Eardwulf (fl.  790 – c. 830) was king of Northumbria from 796 to 806, when he was deposed and went into exile.  He may have had a second reign from 808 until perhaps 811 or 830.  Northumbria in the last years of the eighth century was the scene of dynastic strife between several noble families: in 790, the then-king Æthelred I attempted to have Eardwulf assassinated.  Eardwulf's survival may have been viewed as a sign of divine favour.  A group of nobles conspired to assassinate Æthelred in April 796 and he was succeeded by Osbald: Osbald's reign lasted only twenty-seven days before he was deposed and Eardwulf became king on 14 May 796. Eadred Lulisc or Eadred of Carlisle (fl.  late 9th century) is the abbot of Carlisle recorded by the "Historia de Sancto Cuthberto".  The "Historia" gives the abbot central place in the election of Guthred as king of Northumbria by the Viking army based in Yorkshire, and that subsequently Eadred purchased land from him, using it to endow the bishopric of St Cuthbert.  The "Historia" also related that he and Eardwulf, Bishop of Lindisfarne, moved the body of St Cuthbert away from its previous base at Lindisfarne, tried to take it to Ireland, but failed and took it back to the east, first to Crayke and then to Chester-le-Street. Edmund Ætheling ( ;  1015–17 – possibly 1046, certainly by 1054) was a member of the royal House of Wessex as the son of Edmund Ironside, who briefly ruled as King of England between April and November 1016.  He fought the Danish Vikings under Cnut the Great, but following the Danish victory at the Battle of Assandun in October, it was agreed that Ironside would rule Wessex, while Cnut took Mercia and probably Northumbria.  In November 1016, Ironside died and Cnut became King of all England. Coenwulf (also spelled Cenwulf, Kenulf, or Kenwulph) was King of Mercia from December 796 until his death in 821.  He was a descendant of a sibling of King Penda, who had ruled Mercia in the middle of the 7th century.  He succeeded Ecgfrith, the son of Offa; Ecgfrith only reigned for five months, and Coenwulf ascended to the throne in the same year that Offa died.  In the early years of Coenwulf's reign he had to deal with a revolt in Kent, which had been under Offa's control.  Eadberht Præn returned from exile in Francia to claim the Kentish throne, and Coenwulf was forced to wait for papal support before he could intervene.  When Pope Leo agreed to anathematize Eadberht, Coenwulf invaded and retook the kingdom; Eadberht was taken prisoner, was blinded, and had his hands cut off.  Coenwulf also appears to have lost control of the kingdom of East Anglia during the early part of his reign, as an independent coinage appears under King Eadwald.  Coenwulf's coinage reappears in 805, indicating that the kingdom was again under Mercian control.  Several campaigns of Coenwulf's against the Welsh are recorded, but only one conflict with Northumbria, in 801, though it is likely that Coenwulf continued to support the opponents of the Northumbrian king Eardwulf.

Supporting sentences:
 He may have had a second reign from 808 until perhaps 811 or 830.  Northumbria in the last years of the eighth century was the scene of dynastic strife between several noble families: in 790, the then-king Æthelred I attempted to have Eardwulf assassinated. Æthelred ( ; c. 762  – 18 April 796), was the king of Northumbria from 774 to 779 and again from 790 until he was murdered in 796.  He was the son of Æthelwald Moll and Æthelthryth and possibly became king while still a child after Alhred was deposed.