William Seymour, 3rd Duke of Somerset (17 April 1652 – 12 December 1671) was the son of Henry Seymour, Lord Beauchamp, and Mary Capell. As both his father and two elder uncles had predeceased him, he succeeded to the dukedom on the death of his grandfather William Seymour.
He died in 1671, unmarried and childless and was succeeded by his paternal uncle John Seymour.
Ancestry
| | | | | | | | | Edward Seymour, 1st Earl of Hertford |
| | | | | | | | | Edward Seymour, 1st Earl of Hertford | | | | | | | Edward Seymour, Lord Beauchamp of Hache | | | | | | | | | | Catherine Grey | | | | | | | William Seymour, 2nd Duke of Somerset | | | | | | | | | | | | Sir Richard Rogers | | | | | | | Honora Rogers | | | | | | | | | | Cecilia Luttrell | | | | | | | Henry Seymour, Lord Beauchamp | | | | | | | | | | | | | | Walter Devereux, 1st Earl of Essex | | | | | | | Robert Devereux, 2nd Earl of Essex | | | | | | | | | | Lettice Knollys | | | | | | | Frances Devereux | | | | | | | | | | | | Sir Francis Walsingham | | | | | | | Frances Walsingham | | | | | | | | | | Ursula St. Barbe | | | | | | | William Seymour, 3rd Duke of Somerset | | | | | | | | | | | | | | | | | | | | | | Sir Henry Capell | | | | | | | | | | | | | | | | | Sir Arthur Capell, 1st Baron Capell of Hadham | | | | | | | | | | | | Sir Edward Montagu | | | | | | | Theodosia Montagu | | | | | | | | | | Elizabeth Harrington | | | | | | | Mary Capell | | | | | | | | | | | | | | Sir Charles Morrison | | | | | | | Sir Charles Morrison, 1st Baronet | | | | | | | | | | Dorothea Clark | | | | | | | Elizabeth Morrison | | | | | | | | | | | | Baptist Hicks, 1st Viscount Campden | | | | | | | Mary Hicks | | | | | | | | | | Elizabeth May | | | | | | | | | | | | | | | | | | | |
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| | | | | | | | | Edward Seymour, 1st Earl of Hertford |
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| Edward Seymour, Lord Beauchamp of Hache | |
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| Catherine Grey |
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| William Seymour, 2nd Duke of Somerset | |
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| Sir Richard Rogers |
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| Honora Rogers | |
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| Cecilia Luttrell |
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| Henry Seymour, Lord Beauchamp | |
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| Walter Devereux, 1st Earl of Essex |
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| Robert Devereux, 2nd Earl of Essex | |
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| Lettice Knollys |
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| Frances Devereux | |
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| Sir Francis Walsingham |
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| Frances Walsingham | |
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| Ursula St. Barbe |
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| William Seymour, 3rd Duke of Somerset | |
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| Sir Henry Capell | |
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| Sir Arthur Capell, 1st Baron Capell of Hadham | |
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| Sir Edward Montagu |
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| Theodosia Montagu | |
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| Elizabeth Harrington |
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| Mary Capell | |
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| Sir Charles Morrison |
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| Sir Charles Morrison, 1st Baronet | |
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| Dorothea Clark |
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| Elizabeth Morrison | |
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| Baptist Hicks, 1st Viscount Campden |
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| Mary Hicks | |
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| Elizabeth May |
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| Edward Seymour, Lord Beauchamp of Hache | |
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| Catherine Grey |
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| William Seymour, 2nd Duke of Somerset | |
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| Sir Richard Rogers |
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| Honora Rogers | |
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| Cecilia Luttrell |
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| Henry Seymour, Lord Beauchamp | |
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| Walter Devereux, 1st Earl of Essex |
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| Robert Devereux, 2nd Earl of Essex | |
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| Lettice Knollys |
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| Frances Devereux | |
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| Sir Francis Walsingham |
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| Frances Walsingham | |
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| Ursula St. Barbe |
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| William Seymour, 3rd Duke of Somerset | |
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| Sir Henry Capell | |
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| Sir Arthur Capell, 1st Baron Capell of Hadham | |
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| Sir Edward Montagu |
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| Theodosia Montagu | |
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| Elizabeth Harrington |
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| Mary Capell | |
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| Sir Charles Morrison |
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| Sir Charles Morrison, 1st Baronet | |
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| Dorothea Clark |
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| Elizabeth Morrison | |
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| Baptist Hicks, 1st Viscount Campden |
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| Mary Hicks | |
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| Elizabeth May |
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