The' 'Hon. William Sidney (19 August 1865 - 18 June 1945), known briefly as William Sidney, 5th Baron De L'Isle and Dudley of Penshurst in 1945, was a barrister and local politician in the Chelsea area. The fourth son of Philip Sidney, 2nd Baron De L'Isle and Dudley of Penshurst and Mary née Foulis, he was educated at Eton and Cambridge before being called to the bar at the Inner Temple in 1886. Following the death of his two elder brothers, the 3rd and 4th Barons De L'Isle and Dudley, he succeeded to the title as 5th Baron on 18 April 1945. However, he died suddenly less than two months later.