On 20 Apr 1678 [her uncle] Francis Seymour 5th Duke Somerset 1658-1678 (age 20) was killed. He was unmarried and childless. He was shot dead by Genoese Horatio Botti whose wife Seymour was said to have insulted at Lerici. His brother [her father] Charles Seymour 6th Duke Somerset (age 15) succeeded 6th Duke Somerset, 6th Earl Hertford.
On 27 Mar 1679 Henry Cavendish (age 20) and [her mother] Elizabeth Percy Duchess Somerset (age 12) were married. She being the sole heiress of [her grandfather] Josceline Percy 11th Earl of Northumberland she brought an enormous fortune to the marriage. She the daughter of Josceline Percy 11th Earl of Northumberland and Elizabeth Wriothesley Countess Northumberland 1646-1690 (age 33). He the son of Henry Cavendish 2nd Duke Newcastle upon Tyne (age 48) and Frances Pierrepont Duchess Newcastle upon Tyne 1630-1695 (age 48).
On 15 Nov 1681 Thomas "Tom of Ten Thousand" Thynne (age 33) and [her mother] Elizabeth Percy Duchess Somerset (age 14) were married. She the daughter of Josceline Percy 11th Earl of Northumberland and Elizabeth Wriothesley Countess Northumberland 1646-1690 (age 35).
On 30 May 1682 [her father] Charles Seymour 6th Duke Somerset (age 19) and [her mother] Elizabeth Percy Duchess Somerset (age 15) were married. His first marriage, her third having been widowed twice by the age of seventeen. She by marriage Duchess Somerset. Being the sole heiress of her father [her grandfather] Josceline Percy 11th Earl of Northumberland she brought considerable wealth to the marriage. She the daughter of Josceline Percy 11th Earl of Northumberland and Elizabeth Wriothesley Countess Northumberland 1646-1690 (age 36). He a great x 5 grandson of King Henry VII of England and Ireland.
In 1685 Elizabeth Seymour Countess Thomond was born to Charles Seymour 6th Duke Somerset (age 22) and Elizabeth Percy Duchess Somerset (age 17).
On 02 May 1691 Henry O'Brien 7th Earl Thomond 1620-1691 (age 71) died. His grandson [her future husband] Henry O'Brien 8th Earl Thomond 1688-1741 (age 2) succeeded 8th Earl Thomond.
In 1707 Henry O'Brien 8th Earl Thomond 1688-1741 (age 18) and Elizabeth Seymour Countess Thomond (age 22) were married. She by marriage Countess Thomond. She the daughter of Charles Seymour 6th Duke Somerset (age 44) and Elizabeth Percy Duchess Somerset (age 39). He the son of Henry Horatio O'Brien and Henrietta Somerset Countess Suffolk 1669-1715 (age 38).
Around 1710. Michael Dahl (age 51). Portrait of Elizabeth Seymour Countess Thomond (age 25). Petworth House.
On 24 Nov 1722 [her mother] Elizabeth Percy Duchess Somerset (age 55) died.
On 04 Feb 1725 [her father] Charles Seymour 6th Duke Somerset (age 62) and [her step-mother] Charlotte Finch Duchess Somerset 1693-1773 (age 32) were married. She by marriage Duchess Somerset. The difference in their ages was 30 years. She the daughter of Daniel Finch 2nd Earl Nottingham 7th Earl Winchilsea (age 77) and Anne Hatton Countess Nottingham and Winchelsea -1743. He a great x 5 grandson of King Henry VII of England and Ireland. 
On 02 Apr 1734 Elizabeth Seymour Countess Thomond (age 49) died.
On 20 Apr 1741 [her former husband] Henry O'Brien 8th Earl Thomond 1688-1741 (age 52) died without issue. He was buried in St Mary's Cathedral, Limerick, County Limerick.
Paternal Family Tree: Seymour
Maternal Family Tree: Audrey Saunders 1551-1588
Kings Wessex: Great x 20 Grand Daughter of King Edmund "Ironside" I of England
Kings Gwynedd: Great x 17 Grand Daughter of Owain "Great" King Gwynedd 1100-1170
Kings Seisyllwg: Great x 22 Grand Daughter of Hywel "Dda aka Good" King Seisyllwg King Deheubarth
Kings Powys: Great x 17 Grand Daughter of Maredudd ap Bleddyn King Powys 1047-1132
Kings England: Great x 6 Grand Daughter of King Henry VII of England and Ireland
Kings Scotland: Great x 15 Grand Daughter of William "Lion" I King Scotland
Kings Franks: Great x 16 Grand Daughter of Louis VII King Franks
Kings France: Great x 9 Grand Daughter of Charles "Beloved Mad" VI King France
Great x 4 Grandfather: Edward Seymour 1st Duke Somerset 6 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Edward Seymour 1st Earl Hertford 5 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Anne Stanhope Duchess Somerset
4 x Great Grand Daughter of King Edward III of England
Great x 2 Grandfather: Edward Seymour 2 x Great Grand Son of King Henry VII of England and Ireland
Great x 4 Grandfather: Henry Grey 1st Duke of Suffolk
5 x Great Grand Son of King Edward III of England
Great x 3 Grandmother: Catherine Grey Countess Hertford Great Grand Daughter of King Henry VII of England and Ireland
Great x 4 Grandmother: Frances Brandon Duchess of Suffolk
Grand Daughter of King Henry VII of England and Ireland
Great x 1 Grandfather: Francis Seymour 1st Baron Seymour Trowbridge 3 x Great Grand Son of King Henry VII of England and Ireland
Great x 2 Grandmother: Honora Rogers
GrandFather: Charles Seymour 2nd Baron Seymour Trowbridge 4 x Great Grand Son of King Henry VII of England and Ireland
Great x 2 Grandfather: Gilbert Prynne of Allington
Great x 1 Grandmother: Frances Prynne 7 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: John Carey
4 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Wymond Carey 5 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Joyce Denny
7 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 2 Grandmother: Jane Davys 6 x Great Grand Daughter of King Edward III of England
Father: Charles Seymour 6th Duke Somerset 5 x Great Grand Son of King Henry VII of England and Ireland
Great x 4 Grandfather: Robert Alington 9 x Great Grand Son of King Edward "Longshanks" I of England
Great x 3 Grandfather: Giles Alington 10 x Great Grand Son of King Edward "Longshanks" I of England
Great x 2 Grandfather: Giles Alington 11 x Great Grand Son of King Edward "Longshanks" I of England
Great x 1 Grandfather: William Alington 1st Baron Alington 12 x Great Grand Son of King Edward "Longshanks" I of England
GrandMother: Eizabeth Alington 2nd Baroness Seymour Trowbridge 8 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Lionel Tollemache
Great x 3 Grandfather: Lionel Tollemache 1st Baronet
Great x 4 Grandmother: Susan Jermyn
Great x 2 Grandfather: Lionel Tollemache 2nd Baronet 8 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Henry Cromwell 2nd Baron Cromwell Oakham
7 x Great Grand Son of King Edward III of England
Great x 3 Grandmother: Katherine Cromwell 7 x Great Grand Daughter of King Edward III of England
Great x 4 Grandmother: Mary Paulett Baroness Cromwell Oakham
6 x Great Grand Daughter of King Edward III of England
Great x 1 Grandmother: Elizabeth Tollemache Baroness Alington 7 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Michael Stanhope 4 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: John Stanhope 1st Baron Stanhope 5 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Anne Rawson
Great x 2 Grandmother: Elizabeth Stanhope Lady Talmash 6 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Henry Macwilliams
Great x 3 Grandmother: Margaret Macwilliams Baroness Stanhope
Elizabeth Seymour Countess Thomond 1685-1734 6 x Great Grand Daughter of King Henry VII of England and Ireland
Great x 4 Grandfather: Thomas Percy 4 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Henry Percy 8th Earl of Northumberland 5 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Eleanor Harbottle 5 x Great Grand Daughter of King Edward III of England
Great x 2 Grandfather: Henry "Wizard Earl" Percy 9th Earl of Northumberland 6 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: John Neville 4th Baron Latimer of Snape 5 x Great Grand Son of King Edward III of England
Great x 3 Grandmother: Katherine Neville Countess Northumberland 6 x Great Grand Daughter of King Edward III of England
Great x 4 Grandmother: Lucy Somerset Baroness Latimer Snape 5 x Great Grand Daughter of King Edward III of England
Great x 1 Grandfather: Algernon Percy 10th Earl of Northumberland 7 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Richard Devereux
5 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Walter Devereux 1st Earl Essex 6 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Dorothy Hastings
5 x Great Grand Daughter of King Edward III of England
Great x 2 Grandmother: Dorothy Devereux Countess Northumberland 7 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Francis Knollys
Great x 3 Grandmother: Lettice Knollys Countess Essex 6 x Great Grand Daughter of King Edward III of England
Great x 4 Grandmother: Catherine Carey 5 x Great Grand Daughter of King Edward III of England
GrandFather: Josceline Percy 11th Earl of Northumberland 8 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Thomas Howard 4th Duke of Norfolk
7 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Thomas Howard 1st Earl Suffolk 7 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Margaret Audley Duchess Norfolk
6 x Great Grand Daughter of King Edward III of England
Great x 2 Grandfather: Theophilus Howard 2nd Earl Suffolk 8 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Henry Knyvet
8 x Great Grand Son of King Edward "Longshanks" I of England
Great x 3 Grandmother: Catherine Knyvet Countess Suffolk 9 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 4 Grandmother: Elizabeth Stumpe
Great x 1 Grandmother: Elizabeth Howard Countess Northumberland 9 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Alexander Manderston Home
Great x 3 Grandfather: George Home 1st Earl Dunbar
Great x 2 Grandmother: Elizabeth Home Countess Suffolk 1599-1633 18 x Great Grand Daughter of King Henry I "Beauclerc" England
Great x 4 Grandfather: Alexander Gordon 3rd of Gight 16 x Great Grand Son of King Henry I "Beauclerc" England
Great x 3 Grandmother: Elizabeth Gordon Countess Dunbar 1575-1645 17 x Great Grand Daughter of King Henry I "Beauclerc" England
Great x 4 Grandmother: Agnes Beaton
Mother: Elizabeth Percy Duchess Somerset 9 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Thomas Wriothesley 1st Earl of Southampton
Great x 3 Grandfather: Henry Wriothesley 2nd Earl of Southampton
Great x 4 Grandmother: Jane Cheney Countess Southampton 1509-1574
Great x 2 Grandfather: Henry Wriothesley 3rd Earl of Southampton 7 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Anthony Browne 1st Viscount Montagu
5 x Great Grand Son of King Edward III of England
Great x 3 Grandmother: Mary Browne Countess Southampton 6 x Great Grand Daughter of King Edward III of England
Great x 4 Grandmother: Jane Radclyffe
6 x Great Grand Daughter of King Edward III of England
Great x 1 Grandfather: Thomas Wriothesley 4th Earl of Southampton 2nd Earl Chichester 7 x Great Grand Son of Henry IV King England
Great x 4 Grandfather: George Vernon
4 x Great Grand Son of Henry IV King England
Great x 3 Grandfather: John Vernon 5 x Great Grand Son of Henry IV King England
Great x 2 Grandmother: Elizabeth Vernon Countess Southampton 1572-1655 6 x Great Grand Daughter of Henry IV King England
GrandMother: Elizabeth Wriothesley Countess Northumberland 1646-1690 8 x Great Grand Daughter of Henry IV King England
Great x 4 Grandfather: William Leigh
Great x 3 Grandfather: Francis Leigh
Great x 4 Grandmother: Frances Harrington
Great x 2 Grandfather: Francis Leigh 1st Earl Chichester
Great x 4 Grandfather: Thomas Egerton 1st Viscount Brackley
Great x 3 Grandmother: Mary Egerton
Great x 4 Grandmother: Elizabeth Ravenscroft
Great x 1 Grandmother: Elizabeth Leigh Countess Southampton 1620-1655 13 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 4 Grandfather: Henry Boteler 10 x Great Grand Son of King Edward "Longshanks" I of England
Great x 3 Grandfather: John Boteler 1st Baron Boteler 11 x Great Grand Son of King Edward "Longshanks" I of England
Great x 4 Grandmother: Catherine Waller
Great x 2 Grandmother: Audrey Boteler Countess Chichester 12 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 4 Grandfather: George Villiers of Brokesby
Great x 3 Grandmother: Elizabeth Villiers Baroness Boteler Brantfield
Great x 4 Grandmother: Audrey Saunders