On 01 Nov 1835 [his grandfather] (age 49) died. His son [his father] (age 12) succeeded 3rd Earl Nelson of Trafalgar and Merson in Surrey, 3rd Viscount Merton.
On 28 Jul 1845 [his father] (age 21) and [his mother] Mary Jane Agar Countess Nelson (age 23) were married at St George's Church, Hanover Square. She the daughter of Welbore Ellis Agar 2nd Earl Normanton 1778-1868 (age 67) and Diana Herbert Countess Normanton 1790-1841. He the son of . She a great x 4 granddaughter of King Charles II of England Scotland and Ireland. 
On 21 Dec 1857 Thomas Nelson 4th Earl Nelson was born to (age 34) and Mary Jane Agar Countess Nelson (age 35).
On 08 May 1904 [his mother] Mary Jane Agar Countess Nelson (age 81) died at Trafalgar House Salisbury, Wiltshire [Map].
On 25 Feb 1913 [his father] (age 89) died. His son Thomas Nelson 4th Earl Nelson (age 55) succeeded 4th Earl Nelson of Trafalgar and Merson in Surrey, 4th Viscount Merton.
On 30 Sep 1947 Thomas Nelson 4th Earl Nelson (age 89) died. His brother [his brother] (age 87) succeeded 5th Earl Nelson of Trafalgar and Merson in Surrey, 5th Viscount Merton.
Maternal Family Tree: Elizabeth Trevor Duchess Marlborough 1713-1761
Kings Wessex: Great x 24 Grand Son of King Edmund "Ironside" I of England
Kings Gwynedd: Great x 21 Grand Son of Owain "Great" King Gwynedd 1100-1170
Kings Seisyllwg: Great x 26 Grand Son of Hywel "Dda aka Good" King Seisyllwg King Deheubarth
Kings Powys: Great x 22 Grand Son of Maredudd ap Bleddyn King Powys 1047-1132
Kings England: Great x 5 Grand Son of King Charles II of England Scotland and Ireland
Kings Scotland: Great x 17 Grand Son of Robert "The Bruce" I King Scotland
Kings Franks: Great x 20 Grand Son of Louis VII King Franks
Kings France: Great x 7 Grand Son of Henry IV King France
Great x 1 Grandfather: Thomas Bolton of Wells Norfolk
Great x 2 Grandfather: Reverend Edmund Nelson
Great x 1 Grandmother: Susannah Nelson
5 x Great Grand Son of King Charles II of England Scotland and Ireland
Great x 4 Grandfather: Charles Agar
Great x 3 Grandfather: James Agar
Great x 4 Grandmother: Ellis Blanchville
Great x 2 Grandfather: Henry Agar
Great x 4 Grandfather: Henry Wemyss of Danesfort
Great x 3 Grandmother: Mary Wemyss
Great x 1 Grandfather: Charles Agar 1st Earl Normanton
Great x 4 Grandfather: Reverend John Ellis
Great x 3 Grandfather: Bishop Welbore Ellis
Great x 2 Grandmother: Anne Ellis
Great x 4 Grandfather: John Briscoe of Boughton in Northamptonshire
Great x 3 Grandmother: Diana Briscoe
GrandFather: Welbore Ellis Agar 2nd Earl Normanton 1778-1868
Mother: Mary Jane Agar Countess Nelson 4 x Great Grand Daughter of King Charles II of England Scotland and Ireland
Great x 4 Grandfather: Thomas Herbert 8th Earl Pembroke 5th Earl Montgomery 9 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Henry Herbert 6th Earl Montgomery 9th Earl Pembroke 10 x Great Grand Son of King Edward III of England
Great x 2 Grandfather: Henry Herbert 10th Earl Pembroke 7th Earl Montgomery 1734-1794 11 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Richard Fitzwilliam 5th Viscount Fitzwilliam 14 x Great Grand Son of King Edward "Longshanks" I of England
Great x 3 Grandmother: Mary Fitzwilliam Countess Pembroke and Montgomery 1707-1769 10 x Great Grand Daughter of King Edward III of England
Great x 4 Grandmother: Frances Shelley Viscountess Fitzwilliam 9 x Great Grand Daughter of King Edward III of England
Great x 1 Grandfather: George Augustus Herbert 11th Earl Pembroke 8th Earl Montgomery 12 x Great Grand Son of King Edward III of England
Great x 4 Grandfather: Charles Spencer 3rd Earl of Sunderland
10 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Charles Spencer 3rd Duke of Marlborough 11 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Anne Churchill Countess Sunderland 1683-1716
15 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 2 Grandmother: Elizabeth Spencer Countess Pembroke and Montgomery 1737-1831 12 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Thomas Trevor 2nd Baron Trevor Bromham
Great x 3 Grandmother: Elizabeth Trevor Duchess of Marlborough 1713-1761
GrandMother: Diana Herbert Countess Normanton 1790-1841 3 x Great Grand Daughter of King Charles II of England Scotland and Ireland
Great x 4 Grandfather: Charles Beauclerk 1st Duke St Albans
Son of King Charles II of England Scotland and Ireland
Great x 3 Grandfather: Sidney Beauclerk Grand Son of King Charles II of England Scotland and Ireland
Great x 4 Grandmother: Diana Vere Duchess St Albans 1679-1742
10 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 2 Grandfather: Topham Beauclerk Great Grand Son of King Charles II of England Scotland and Ireland
Great x 4 Grandfather: Thomas Norris 12 x Great Grand Son of King Edward "Longshanks" I of England
Great x 3 Grandmother: Mary Norris 13 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 1 Grandmother: Elisabeth Beauclerk 2 x Great Grand Daughter of King Charles II of England Scotland and Ireland
Great x 4 Grandfather: Charles Spencer 3rd Earl of Sunderland 10 x Great Grand Son of King Edward III of England
Great x 3 Grandfather: Charles Spencer 3rd Duke of Marlborough 11 x Great Grand Son of King Edward III of England
Great x 4 Grandmother: Anne Churchill Countess Sunderland 1683-1716 15 x Great Grand Daughter of King Edward "Longshanks" I of England
Great x 2 Grandmother: Diana Spencer Viscountess St John and Bolingbroke 12 x Great Grand Daughter of King Edward III of England
Great x 4 Grandfather: Thomas Trevor 2nd Baron Trevor Bromham
Great x 3 Grandmother: Elizabeth Trevor Duchess of Marlborough 1713-1761