Edward Adolphus Ferdinand Seymour, Earl St. Maur (17 July 1835 – Dover Street, London, 30 September 1869), also 13th Baron Seymour in his own right, was a British aristocrat and soldier.
Seymour was the eldest son of Edward Seymour, 12th Duke of Somerset, and Georgiana Sheridan. He was styled Lord Seymour until 1863 when his father was created Earl St Maur, of Berry Pomeroy, and he adopted his father's new creation as a courtesy title. He was commonly known as Ferdy.
Seymour briefly fought as a volunteer in the Anglo-Persian War (1855–1857) and almost immediately afterwards, was at the Relief of Lucknow during the Indian Mutiny (1857–1858). He fought in Italy and Sicily, as a civilian volunteer, joining Giuseppe Garibaldi's Essercito Meridionale (Southern Army) as a private in 1860. At an early stage he assumed the rank of Captain on the basis that along with his younger brother Lord Edward Seymour (1841–1865) he had co-commanded Volunteer Cavalry in England; both brothers assuming the rank of Captain. He distinguished himself in the Volturno campaign in late 1860 and in other campaigns. Garibaldi later officially conferred him with the rank of Captain despite the fact that Seymour was merely a civilian volunteer, and he assumed the name pseudonym "Captain Richard Sarsfield" in commemoration of a hero he had heard about when at Christ Church, Oxford.
In late 1860, after Garibaldi had appointed Seymour as his "Military Secretary", he accused a brother officer (who happened to be a favourite of Garibaldi's) of embezzling Garibaldi funds, the said brother officer challenged Seymour to a duel that his superior officer (Colonel John Whitehead Peard - Garibaldi's "Englishman") forbade him to attend. Seymour felt it necessary to be accompanied at all times by bodyguards and to escape back to Britain - which he did. The scandal induced Seymour to give up any thought of involvement in warfare and he was never again to partake in warfare, choosing to travel extensively throughout Europe and study languages, seldom returning home, much to the resentment of his family.