Frederick William Brook Thellusson, 5th Baron Rendlesham JP DL (9 February 1840 – 9 November 1911), was a British Conservative politician.

[5] Reportedly a fine footballer at Eton and Oxford, he maintained a keen interest in other sports in later life, being on the National Hunt Committee as well as a member of the Jockey Club and the Royal Yacht Squadron.

[6] On 12 February 1887 he was appointed Honorary Colonel of the Suffolk Artillery Militia, and retained the position until the unit was disbanded in 1909.

[10][11] In 1861, Lord Rendlesham was married to Lady Egidia Montgomerie (c. 1843–1880) at St Peter's Church, Eaton Square followed by a honeymoon at Peckforton Castle, the seat of John Tollemache.

[12] She was a daughter of Archibald Montgomerie, 13th Earl of Eglinton and the former Theresa Howe (née Newcomen) Cockerell (widow of Capt.