In the mid-1760s, Lord William had an affair with a married woman,
Lady Sarah Bunbury, who had once been courted by King
George III. In 1768, he fathered a child upon Lady Sarah, a daughter who was not immediately disclaimed by
Sir Charles Bunbury, and received the name Louisa Bunbury. Nevertheless, Lady Sarah and Lord William eloped shortly afterwards, taking the infant with them. Lord William soon tired of his lover's incessant demands for attention, gifts and ceaseless entertainments and abandoned her. Her husband refused to take her back, and Lady Sarah returned to her brother's house with her child, while her husband, Sir Charles, moved Parliament for a divorce on grounds of adultery, citing her elopement, not the birth of Louisa. It was not until 1776 that the decree of divorce was issued. The affair with Lady Sarah ruined both hers and William's social reputation, and also his military and political career. In 1778 he was appointed lieutenant-colonel in his brother's new
fencible regiment 'the Northern regiment of Fencible Men' (Gordon's Fencibles). ==Marriage==