Who was the brother of Tostig Godwinson that overthrew Gruffydd, Rhiwallon, and Bleddyn?
King Harold Godwinson
Title: Rhiwallon ap Cynfyn
Passage: 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".
Title: Tostig Godwinson
Passage: 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.
Title: Judith of Flanders (died 1095)
Passage: Judith of Flanders, Countess of Northumbria, and later Duchess of Bavaria (1030-35 to 5 March 1095) was the wife firstly of Tostig Godwinson, Earl of Northumbria, and secondly of Welf I, Duke of Bavaria.  Her niece was Matilda of Flanders, Queen consort of William the Conqueror, who was Judith's cousin.
Rhiwallon ap Cynfyn Tostig Godwinson