Who married Lady Mary Bruce?

Field Marshal Charles Lennox, 3rd Duke of Richmond, (22 February 1735 – 29 December 1806), styled Earl of March until 1750, was British politician and military officer. Associated with the Rockingham Whigs, Richmond briefly served as Secretary of State for the Southern Department for a three-month period in 1766. His support for the Patriots during the American War of Independence along with concession in Ireland and parliamentary reform in Britain led Richmond to be nicknamed "the Radical Duke". He is believed by many to be the source of the second parchment copy of the United States Declaration of Independence, known as the Sussex Declaration. Richmond went on to be a reforming Master-General of the Ordnance first in the first Rockingham ministry and then in the first Pitt ministry.