Half First Cousin is in Half-First Cousin.
Around 574 Conall mac Comgaill King of Dál Riata -574 died. His half first cousin Áedán mac Gabráin King of Dál Riata 560-609 (14) succeeded King of Dál Riata.
On 12 Oct 633 King Penda's alliance of Gwynedd and Mercia defeated the Northumbrians at the Battle of Hatfield Chase.
Eadfrith Deira -633 was captured.
Edwin King Northumbria 586-633 (47) was killed. His half first cousin Osric King Deira -634 succeeded King Deira. His nephew Eanfrith King Bernicia 590-634 (43) succeeded King Bernicia.
Edwin's son Osfrith Deira -633 was killed.
After 12 Oct 633Eadfrith Deira -633 was killed. His half first cousin Eanfrith King Bernicia 590-634 succeeded King Bernicia.
In 709 Coenred King Mercia -709 abdicated as King Mercia in favour of Ceolred King Mercia -716. His half first cousin Ceolred King Mercia -716 succeeded King Mercia.
In 737 Ceolwulf King Northumbria -760 abdicated. His half first cousin Eadberht King of Northumbria -768 succeeded King Northumbria.
In 900 Donald II King Alba -900 died. His half first cousin Constantine II King Alba -952 succeeded King Alba.
Around 25 Mar 1005 Kenneth III King Alba 966-1005 (39) died. His half first cousin Malcolm II King Alba 954-1034 (51) succeeded King Alba.
On 03 Jun 1253 Margaret Beaumont 7th Countess Warwick -1253 died. Her half first cousin William Maudit 8th Earl Warwick 1220-1268 (33) succeeded 8th Earl Warwick 1C 1088. Alice Segrave Countess Warwick 1232- (21) by marriage Countess Warwick.
On 22 Sep 1629 Robert Radclyffe 5th Earl of Sussex 1573-1629 (56) died at Clerkenwell. His first cousin once removed Edward Radclyffe 6th Earl of Sussex 1559-1643 (70) succeeded 6th Earl of Sussex. His half first cousin Henry Mildmay 15th Baron Fitzwalter 1585- (44) de jure 15th Baron Fitzwalter.
In Jul 1657 Ulick Burke 1st Marquess Clanricarde 1604-1657 (53) died. His half first cousin Richard Burke 6th Earl Clanricarde -1666 succeeded 6th Earl Clanricarde.
In 1674 Thomas Dillon 5th Viscount Dillon -1674 died. His half first cousin Lucas Dillon 6th Viscount Dillon -1682 succeeded 6th Viscount Dillon of Costello Gallen in Mayo.
On 12 Sep 1685 Edmund Bacon 4th Baronet Bacon 1633-1685 (52) died. His half first cousin Robert Bacon 5th Baronet Bacon 1652-1704 (33) succeeded 5th Baronet Bacon of Redgrave.
In 1686 William Clifton 3rd Baronet Clifton 1663-1686 (22) died. His half first cousin Gervase Clifton 4th Baronet Clifton 1666-1731 (20) succeeded 4th Baronet Clifton of Clifton in Nottinghamshire.
On 21 Sep 1690 Wriothesley Baptist Noel 2nd Earl Gainsborough 1661-1690 (29) died. His half first cousin Baptist Noel 3rd Earl Gainsborough 1684-1714 (6) succeeded 3rd Earl Gainsborough 1C 1682.
In 1692 Colonel Robert Carey 6th Baron Hunsdon 1652-1692 (40) died. His half first cousin Robert Carey 7th Baron Hunsdon 1649-1702 (43) succeeded 7th Baron Hunsdon.
On 10 Nov 1705 Alexander Bruce 3rd Earl Kincardine 1666-1705 (39) died. His half first cousin Alexander Bruce 4th Earl Kincardine -1706 succeeded 4th Earl Kincardine.
In 1737 Richard Dillon 9th Viscount Dillon -1737 died. His half first cousin Charles Dillon 10th Viscount Dillon -1741 succeeded 10th Viscount Dillon of Costello Gallen in Mayo.
On 02 Jan 1741 Edward Littleton 3rd Baronet -1742 died. His half first cousin Edward Littleton MP 4th Baronet Pillaton Hall 1727-1812 (14) succeeded 4th Baronet Littleton of Pillaton Hall.
On 16 Jun 1741 Edward Harley 2nd Earl Oxford and Earl Mortimer 1689-1741 (52) died. His half first cousin Edward Harley 3rd Earl Oxford and Earl Mortimer 1699-1755 (42) succeeded 4th Earl Oxford and Earl Mortimer. Susanna Archer Countess Oxford and Countess Mortimer 1728- (13) by marriage Countess Oxford and Countess Mortimer.
In 1747 Robert Worsley 4th Baronet 1670-1747 (77) died. His half first cousin James Worsley 5th Baronet 1672-1756 (75) succeeded 5th Baronet Worsley of Appuldurcombe.
On 24 Jun 1766 John Butler 15th Earl Ormonde -1766 died. His half first cousin Walter Butler 16th Earl Ormonde 9th Earl Ossory 1703-1783 (63) de jure 16th Earl Ormonde, 9th Earl Ossory although he never used these titles.
In 1768 Robert Hicks 4th Baronet -1768 died. His half first cousin John Baptist Hicks 5th Baronet 1721-1792 (47) succeeded 5th Baronet Beverston.
On 27 Jul 1768 William Dalrymple Crichton 5th Earl Dumfries 4th Earl of Stair 1699-1768 (69) died. Patrick Mcdouall Crichton 6th Earl Dumfries 1726-1803 (41) succeeded 6th Earl Dumfries. His half first cousin John Dalrymple 5th Earl of Stair 1720-1789 (48) succeeded 4th Earl of Stair.
On 10 Mar 1791 William Wentworth 2nd Earl Strafford 1722-1791 (68) died. His half first cousin Frederick Wentworth 3rd Earl Strafford 1732-1799 (59) succeeded 3rd Earl Strafford 2C 1711.
On 09 Dec 1826 John Evelyn Pierrepont Dormer 10th Baron Dormer 1771-1826 (55) died. His half first cousin Joseph Thaddeus Dormer 11th Baron Dormer 1790-1871 (36) succeeded 11th Baron Dormer.
On 17 Jul 1827 George Douglas 16th Earl Morton 1761-1827 (66) died. His half first cousin George Sholto Douglas 17th Earl Morton 1789-1858 (37) succeeded 17th Earl Morton.
On 14 Oct 1827 Frederick North 5th Earl Guildford 1766-1827 (61) died. His half first cousin Francis North 6th Earl Guildford 1772-1861 (54) succeeded 6th Earl Guildford 3C 1752, 12th Baron North, 8th Baron Guildford.
On 31 Mar 1847 William Eardley-Twisleton-Fiennes 9th or 15th Baron Saye and Sele 1798-1847 (48) died. His half first cousin Frederick Twisleton-Wykeham-Fiennes 10th or 16th Baron Saye and Sele 1799-1887 (47) succeeded 10th or 16th Baron Saye and Sele.
On 29 Aug 1852 George Boscawen 2nd Earl Falmouth 1811-1852 (41) died without issue. Earl Falmouth 2C 1821 extinct. His half first cousin Evelyn Boscawen 6th Viscount Falmouth 1819-1889 (33) succeeded 6th Viscount Falmouth.
On 19 Jul 1860 John Elphinstone 13th Lord Elphinstone 1807-1860 (53) died at King Street. His half first cousin John Elphinstone-Fleming 14th Lord Elphinstone 1819-1861 (40) succeeded 14th Lord Elphinstone.
In 1887 George Lewis Wilmot 5th Baronet Wilmot 1825-1887 (62) died. His half first cousin Robert Rodney Wilmot 6th Baronet Wilmot 1853-1931 (33) succeeded 6th Baronet Wilmot of Osmaston in Derbyshire.
On 28 Jan 1890 Chandos Stanhope Reade 8th Baronet 1851-1868 (38) died at Meldreth. His half first cousin George Compton Reade 9th Baronet 1845-1908 (44) succeeded 9th Baronet Reade of Barton in Berkshire. Melissa Ray Lady Reade -1927 by marriage Lady Reade of Barton in Berkshire.
On 19 Dec 1895 Rainald Knightley 1st Baron Knightley 1819-1895 (76) died without issue. Baron Knightley extinct. His half first cousin Valentine Knightley 4th Baronet 1812-1898 (83) succeeded 4th Baronet Knightley of Fawsley.
In 1914 Benjamin Rupert Chapman 6th Baronet 1865-1914 (49) died. His half first cousin Thomas Chapman 7th Baronet of Killua Castle 1846-1919 (67) succeeded 6th Baronet Chapman of Killua Castle.
On 22 Feb 1963 William Grosvenor 3rd Duke Westminster 1894-1963 (68) died. He was buried at St Mary's Church Eccleston. His half first cousin Gerald Hugh Grosvenor 4th Duke Westminster 1907-1967 (56) succeeded 4th Duke Westminster.
On 11 Sep 1963 Montagu Henry Edmund Cecil Towneley Bertie 8th Earl Abingdon 13th Earl Lindsey 1887-1963 (75) died. His half first cousin Richard Bertie 14th Earl Lindsey 9th Earl Abingdon 1931- (32) succeeded 14th Earl Lindsey, 9th Earl Abingdon.
On 23 Jun 1971 Lyulph Stanley 7th Baron Stanley 1915-1971 (55) died. His half first cousin Thomas Henry Stanley 8th Baron Stanley 1927-2013 (43) succeeded 8th Baron Stanley Alderley, 8th Baron Sheffield of Roscommon in Roscommon.