Peregrine Andrew Mornay Cavendish, 12th Duke of Devonshire (born April 27, 1944), is the elder and only surviving son of the 11th Duke of Devonshire and his wife, the former Deborah Mitford. He succeeded to the Dukedom following the death of his father on 3 May 2004. He held the courtesy title Marquess of Hartington from 1950, when his grandfather the 10th Duke died suddenly of coronary thrombosis, until his succession to the dukedom in 2004.

He is well known in the world of horse racing and serves as Her Majesty's Representative and chairman of Ascot Racecourse Ltd. In 1980 he was elected to the Jockey Club and in 1989 he was appointed its Senior Steward (i.e. Chairman). During his five-year term of office, he oversaw a number of changes within the racing industry, in particular the creation of the British Horseracing Board which is now the governing authority for British racing. He was appointed first Chairman of the Board in June 1993 and retired at the end of his term in 1996.

He was made a CBE for "services to racing" in 1997.

The 12th Duke, as Lord Hartington, married Amanda Carmen Heywood-Lonsdale (also born 1944), a descendant of the Earls of Leven and Melville, on 28 June 1967, and has three children by her:

• William Cavendish, Marquess of Hartington (born 6 June 1969), who is not married. He is a professional photographer.
• The Lady Celina Imogen Carter (born 4 October 1971) who is married to Alexander Kay Corfield Carter, and has issue.
• The Lady Jasmine Nancy Dunne (born 4 May 1973), who has recently married Nicholas Dunne, of landed gentry.

The next heir is a second cousin once removed, Lord Cavendish of Furness , a Life Peer who is the only grandson of Lord Richard Cavendish, a younger brother of the 9th Duke. Lord Cavendish of Furness has one son, also unmarried.

Until May 2004, the 12th Duke and his family were living at Bolton Abbey, one of the Cavendish family estates. With the death of the 11th Duke on May 3, 2004, the 12th Duke and his Duchess may eventually move to Chatsworth House.