In November 1791, The Gentleman’s Magazine recorded the recent marriage at Ostend of William Macintosh’s daughter, Maria (or Mary), to Alexander Augustus, “the Chevalier le Sieur de Colleville, son to the present Marchioness de Colleville, of Normandy, a French officer in the infantry”. Maria, who had been born in Grenada in 1770, was then aged 21. The marriage was a fruitful (and, initially, happy) one. The couple had four children.
In his 1807 will, Macintosh appointed Alexander trustee and attorney together with the Swiss banker, and “old friend”, Jean-Frédéric Perregaux (1744–1808). The trust Macintosh placed in his son in law was, however, misplaced. In 1810 (or possibly 1816) Macintosh was forced to supply a codicil to his will, “revoking and annulling” Alexander’s claim and role. Alexander, it seems, had “abandoned his wife and family and Country in a manner highly disreputable and offensive without having had the least provocation”. With four children to raise alone, Macintosh appointed his daughter “sole heiress of all and whatsoever I may die possessed of in the first place for her own subsistence and the maintenance and education of her four Children”. Macintosh’s will and codicil were proved at London on 13 April 1816. Maria died in 1853.