He married Anne Gore-Booth, daughter of Sir Robert Newcomen Gore-Booth, 3rd Baronet and Hannah Irwin, on 7 December 1829. A son, Robert Edward, was born 18 October 1831, and they had a daughter, Frances Isabella Anna, who died 8 October 1890.
By the mid-1830s, King had suffered a stroke, largely due to the effects of his heavy drinking, and was "almost entirely under the influence of his wife", whose "high-living" was disliked by his father, Viscount Lorton. In 1846, she had formed a relationship with "dubious and insolvent French nobleman", Vicomte Ernest Valentin de Satgé St. Jean; when her son, Henry, was born 31 July 1848, King disowned the child, but he continued to live with his wife and her lover despite his father's protests. King's attempt to sue for divorce in 1850 failed due to his own extramarital affair, with his nursemaid and travelling companion Julie Imhoff, being established.
The King family "were driven to extraordinary lengths" in attempting to stop King's estranged wife and her French lover from gaining control of their property, and so, when on the death of the 7th Earl of Kingston on 21 June 1871, Henry (31 July 1848 – 13 January 1896) succeeded as 8th Earl- his "legitimacy... confirmed (as it could not be disproved) at the probate court in Dublin in 1870"- the "disastrously dispersed hereditary lands" did not come to him with the title.[1]