Henry FitzRoy (born c. 1100-1104, died 1158) was an illegitimate son of Henry I of England by Nest, daughter of Rhys ap Tewdwr, last king of Deheubarth (d. 1093), and his wife, Gwladys ferch Rhiwallon ap Cynfyn.
Nest ferch Rhys (c. 1085 – before 1136) (popularly called Nesta or "Princess Nesta") was the only legitimate daughter of Rhys ap Tewdwr, last king of Deheubarth in Wales, by his wife, Gwladys ferch Rhiwallon ap Cynfyn of Powys.
 Her family is of the House of Dinefwr.
 Nest was the wife of Gerald de Windsor (c. 1075 – 1135), constable of Windsor Castle in Berkshire, by whom she was the ancestress of the FitzGerald dynasty and of the prominent Carew family, of Moulsford in Berkshire, Carew Castle in Pembrokeshire (in the Kingdom of Deheubarth) and of Mohuns Ottery in Devon (see Baron Carew, Earl of Totnes and Carew baronets).
Bleddyn ap Cynfyn (Old Welsh: "Bledẏnt uab Kẏnỽẏn" ;   1073), sometimes spelled Blethyn, was an 11th-century Welsh king.
 He was installed by Harold and Tostig Godwinson as king of Gwynedd in 1063 on his father's death, during their destruction of the kingdom of Bleddyn's half-brother, Gruffydd ap Llywelyn.
 He became king of Powys on his brother Rhiwallon's death in 1069.
 His descendants continued to rule Powys as the House of Mathrafal.
Rhirid Flaidd (sometimes called Rhirid ap Gwrgenau) (fl.
 1160), according to Welsh tradition, was the son of Gwrgenau, who is supported by an obscure and doubtful pedigree going back to Cunedda Wledig, the progenitor of the House of Cunedda which had provided the kings of Gwynedd from the end of Roman Britain until 825.
 The appellation of "blaidd" (wolf) was inherited from his maternal grandmother, Haer, daughter and heiress of Cynfyn, son of Cillyn y Blaidd Rhudd (meaning "Cillyn the Bloody Wolf") of Gest in Eifionydd.
 He was related through his grandmother to Bleddyn ap Cynfyn, king of Powys who rewarded Gwrgenau with land, presumably for his loyalty and service.
Ælfgar (died c. 1060) was the son of Leofric, Earl of Mercia, by his famous mother Godgifu (Lady Godiva).
 He succeeded to his father's title and responsibilities on the latter's death in 1057.
 He gained the additional title of Earl of East Anglia, but also was exiled for a time.
 Through the first marriage of his daughter he would become father-in-law of the Welsh king Gruffydd ap Llywelyn; a few years after his death, his daughter would become a widow and marry English King Harold.
Rhiwallon ap Cynfyn (c. 1020 – c. 1069 ) was a Welsh King.
 the son of Cynfyn ap Gwerstan and brother of King Bleddyn of Powys.
 Through his mother Angharad, he was half-brother to King Gruffydd ap Llywelyn as well.
 Following the 1063 invasion of Wales by Harold and Tostig Godwinson that overthrew Gruffydd, Rhiwallon and Bleddyn jointly received Powys and Gwynedd on condition of faithfully serving Edward the Confessor "everywhere by water and by land".
Tostig Godwinson ( 1026 – 25 September 1066) was an Anglo-Saxon Earl of Northumbria and brother of King Harold Godwinson.
 After being exiled by his brother, Tostig supported the Norwegian king Harald Hardrada's invasion of England, and was killed at the Battle of Stamford Bridge.
Cynfyn ap Gwerystan (born c. 990) — sometimes spelled Kynvyn, Kynwyn, Cynvyn, or Kynfyn — was a Welsh nobleman, principally known on account of his son Bleddyn ap Cynfyn, who established the House of Mathrafal over Powys as a consequence of a Saxon invasion in 1063.
Rhiryd ap Bleddyn (1049–1088) was a Welsh king of Powys.
 He was a son of Bleddyn ap Cynfyn and Haer verch Cillin.
The Battle of Stamford Bridge took place at the village of Stamford Bridge, East Riding of Yorkshire, in England on 25 September 1066, between an English army under King Harold Godwinson and an invading Norwegian force led by King Harald Hardrada and the English king's brother Tostig Godwinson.
 After a bloody battle, both Hardrada and Tostig along with most of the Norwegians were killed.
 Although Harold Godwinson repelled the Norwegian invaders, his army was defeated by the Normans at Hastings less than three weeks later.
 The battle has traditionally been presented as symbolising the end of the Viking Age, although major Scandinavian campaigns in Britain and Ireland occurred in the following decades, such as those of King Sweyn Estrithson of Denmark in 1069–1070 and King Magnus Barefoot of Norway in 1098 and 1102–1103.

Question: Rhiwallon ap Cynfyn, was a Welsh King, following the 1063 invasion of Wales by Harold and Tostig Godwinson, he was an Anglo-Saxon Earl of which location, that overthrew Gruffydd, Rhiwallon and Bleddyn jointly?
Answer: Northumbria