His parentage is confirmed by the Annals of Ulster which record that "Brian son of Ceinnéitig son of Lorcán king of Ireland and Mael Sechnaill son of Domnall king of Temair" led an army to “Áth Cliath” in 1014.
Mathgamain mac Cennétig, King of Munster abt 970 — 976. Mathgamuin son of Cennétig, king of Caisel, was killed by Mael Muad son of Bran, previous king of Munster. [descendants: McMahon family of County Clare (Thomond).]
Lachtna, d. 953
175th MONARCH (High King) of All IRELAND; 53rd King of MUNSTER; (Gormlaith's 3rd husband)
Occupation: High King of Ireland
Marriage and Issue
Brian married four women:
1. Mór, (daughter of the king of Uí Fiachrach Aidne of Connacht) mother of Murchad (Morough), who was slain with Boru at Clontarf.
2. Echrad daughter of the king of Uí Áeda Odba, an obscure branch of the southern Uí Néill, was the mother of Tadc, whose son Toirdelbach and grandson Muirchertach rivalled Brian in power and fame.
3. Gormflaith, the best known of his wives and said to be the most beautiful. She was the daughter of Murchad mac Finn, King of Leinster, sister of Máel Morda and also widow of Olaf Cuaran, the Viking king of Dublin and York. She was the mother of Donnchad, later King of Munster. She was said to be his true love; having mistakeningly challenged his authority one too many times, they divorced. Though she is said to be the cause of his death, she was also said to be the one to mourn him the most.
4. Dub Choblaig, was daughter of the King of Connacht. They had a son Cénnetig mac Briain (Kennedy).
(It's possible Môr, Echrad, Dub were close relatives)
For her third marriage, Gormlaith, d. 1030, (daughter of Murchad mac Finn, a Leinster King of the Uí Fháeláin line) married Brían Bóruma, they had:
Bé Binn, who married Flaithbertach, king of the northern Uí Néill (d. 1036)U1073.1 - Bé Binn daughter of Brian died on pilgrimage in Ard Macha. The Annals of Ulster.
997 Division of Ireland
The Annals of Inisfallen record that "Brian son of Cennétig…and Mael Sechnaill son of Domnall king of Temuir” divided Ireland between them in 997 “Leth Cuinn to Mael Sechnaill and Leth Moga to Brian”. 
1002 High King of Ireland
High King of Ireland 1002. It would appear that Brian´s high-kingship overlapped with that of MaelSechanaill as no record has been found that the latter resigned the position. 
The Annals of Tigernach record that “Brían Boroma regnat” in [999/1000].
The Chronicon of Mariano Scotti records that "Brian rex Hiberniæ" was killed "1014 IX Kal Mai". 
Orkneyinga Saga records that Sigurd Jarl of Orkney went to Ireland “five years after the Battle of Svoldur” to support “King Sigtrygg Silk-Beard” against “King Brian of Ireland”, and left “his elder sons in charge of the earldom”, but was killed in the battle in which King Brian was killed. 
The Annals of Ulster record that "Brian son of Ceinnéitig son of Lorcán king of Ireland and Mael Sechnaill son of Domnall king of Temair" led an army to “Áth Cliath” in 1014, adding that Brian was killed in the battle. 
1014 Great warfare between Brian and the foreigners of Áth Cliath, and Brian then brought a great muster of the men of Ireland to Áth Cliath. After that the foreigners of Áth Cliath gave battle to Brian, son of Cennétig, and he was slain, with his son Murchad, royal heir of Ireland, and Murchad's son, namely, Tairdelbach, as also the princes of Mumu round Conaing, son of Donn Cúán, and round Domnall son of Diarmait, king of Corcu Bascinn, and round Mac Bethad son of Muiredach, king of Ciarraige Luachra, and also Tadc Ua Cellaig, king of Uí Maine, and many others. There were also slain in that battle Mael Mórda son of Murchad, king of Laigin, together with the princes of the Laigin round him, and the foreigners of the western world were slaughtered in the same battle.
23 April 1014, Battle of Clontarf
Brian was too old to fight and his son, Murchad, led the troops and defeated the Norse at the battle near Dublin. Brian was inadequately guarded and was killed by the Norse. 
Annala Uladh: Introduction and index, by B. MacCarthy. Volume 4 of Annala Uladh: Annals of Ulster, otherwise, Annala Senait, Annals of Senat; a chronicle of Irish affairs from A.D. 431, to A.D. 1540, Royal Irish Academy. Volume 4 of Annala Uladh, Cathal MacMaghnusa Maguire]. Authors: Annals of Ulster, Cathal MacMaghnusa Maguire, Royal Irish Academy. Editors : William Maunsell Hennessy, Bartholomew MacCarthy. Publisher: Printed for H. M. Stationery off., by A. Thom & co. (limited), 1901. Original: from the University of Michigan. Digitized: Jun 17, 2008
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