A slightly larger signed version of the miniature was in the Brewster collection, sold Sotheby's, Geneva, 15 November 1995, lot 280.
Ferdinand IV, third son of Charles III, King of Spain, married Archduchess Maria Carolina of Habsburg in 1768 and secondly, in 1814, Donna Lucia Migliaccio, Duchess of Floridia. William Beckford described Ferdinand IV thus: 'His Majesty seemed to eye nothing but the end of his nose, which is doubtless a capital object. Though people have imagined him a weak monarch, I beg leave to differ in opinion, since he has the boldness to prolong his childhood and be happy, in spite of years and conviction. Give him a boar to stab, a pigeon to shot at, a battledore or an angling rod, and he is better contented than Solomon in all his glory, and will never discover, like that sapient sovereign, that all is vanity and vexation of spirit' (R. Hudson [ed.], The Grand Tour 1592-1796, London, 1993, pp. 190-191).