The Earl of Berkeley's eldest son was ruled illegitimate in 1811 after the church register entry for a secret 1785 marriage proved forged

Frederick Augustus, 5th Earl of Berkeley, lived with Mary Cole, daughter of a publican and butcher. They had seven sons and five daughters. Their earliest proven marriage was at Lambeth Church on 16 May 1796, when she was pregnant with their seventh child. Six children were born before it, the eldest, William, in 1786. In 1801 the earl declared that he had married Mary privately at Berkeley in 1785. That would have made William his heir. The earl died in 1810. His will settled Berkeley Castle and its estates on William. The Lords Committee for Privileges tested the 1785 claim in 1811, and the parish register entry was shown to be a forgery. William's claim to the earldom failed. Thomas Moreton, the first son born after the 1796 marriage, was earl in law. He never used the title and never took his seat. Under his father's will he would have lost his own small inheritance had he disputed William's claim. William kept the castle, was made Baron Segrave in 1831 and Earl FitzHardinge in 1841, and died unmarried in 1857. His brother Maurice tried for the barony, failed, and was made Baron FitzHardinge in 1861. The earldom passed to a cousin's line and ended with the 8th Earl, who died in 1942 and left the castle to a distant cousin. In 2026 Berkeley Castle belongs to Charles Berkeley, who inherited it from his father in 2017.