Charles Tennyson d'Eyncourt (20 July 1784 – 21 July 1861), born Charles Tennyson, was a British politician, landowner and Member of Parliament (MP) for Stamford from 1831 to 1832 and for Lambeth from 1832 to 1852. He is also known for his social pretensions and his graceless behaviour towards his nephew, the poet Alfred Lord Tennyson. He was educated at St John's College, Cambridge.
He was the younger son of George Tennyson, who bought the family seat of Beacons, in the village of Tealby, Lincolnshire, along with 2,000 acres (8 km²) of land, and came in time to own a large part of the village. George, as is well known, disinherited his elder son George Clayton Tennyson, the poet’s father, at the age of 12, putting him into a career in the Church, for which he felt no calling; and bestowed all his fortune on Charles.
As a result, there was bad blood between the penurious Tennysons of Somersby, where George Clayton Tennyson had the living until he succumbed to drink and depression, and the opulent Tennysons of Beacons, who fancied themselves not only the wealthy but the socially superior side of the family. Old George’s wife Elizabeth Clayton was supposed to have descended from the Lords of Lovel and d’Eyncourt, and also from King Edward III.
A ruined castle was part of the property, and Charles wished to establish a noble lineage for himself with a title and a castle. When his father died he changed his family’s name to Tennyson d'Eyncourt. Beacons was renamed Bayons, to make it sound like a Norman castle, and it was extensively enlarged and rebuilt in the style of a Gothic castellated manor-house.
In public life Charles Tennyson d'Eyncourt was for many years MP for Lambeth, and was made a Privy Counsellor in 1832. Also in the 1830s, along with Augustus, Duke of Sussex and Admiral Sir Sidney Smith, he was one of the prime movers in a plan to have the Order of Knights Templar revived as a British order of chivalry. In this he failed, and he also failed during 1839-41 in an attempt to revive the d'Eyncourt peerage for himself and his heirs. In February 1829 he was elected a Fellow of the Royal Society