at Exeter with a large following. William is said to have intended him for high promotion, but he died at his seat of Orchard Portman, near Taunton, on 20 March 1690. Sir William was elected a Fellow of the Royal Society on 28 December 1664. Family and heirs He married three times, but had no issue. He married firstly in 1661, Elizabeth, daughter and coheiress of Sir John Cutler, 1st Baronet by his first wife; secondly in 1674, Elizabeth, the daughter and coheiress of Thomas Southcote of Buckland Tout Saints, Devon and thirdly in 1682, Mary, the daughter and heiress of Sir John Holman, 1st Baronet of Banbury, Oxfordshire. He left his valuable estate to his first cousin Henry Seymour (d. 1728), the 5th son of his aunt Anne Portman (d.1695) and her husband Sir Edward Seymour, 3rd Baronet (d.1688). Henry Seymour assumed the name and arms of Portman, and although twice married, left no male progeny. Under Sir William's will his next heir was another cousin, William Berkeley (d.1737) of Pylle, Somerset, great-grandson of his other aunt, Joan Portman, sister of Anne Portman (d.1695). Joan had married Sir George Speke of Whitelackington, Somerset, and their daughter Philippa Speke became the wife of Edward Berkeley (d.1669) of Pylle, 4th in descent in a junior line from Richard Berkeley (d.1514) of Stoke Gifford, Gloucestershire, which manor had been granted in 1337 by Maurice de Berkeley, 2nd Baron Berkeley(1271-1326) to his second son Maurice de Berkeley (d.1347). Philippa's son was Edward Berkeley (d.1707) MP, of Pylle, who married Elizabeth Ryves, daughter of John Ryves of Ranston, Dorset. Their second son was William Berkeley (d.1737) of Pylle (who was heir to his elder brother Maurice Berkeley (d.1717) MP of Pylle) who became in 1728 the second heir of Sir William Portman, 6th Baronet, who like his first heir Henry Seymour, changed his surname to Portman and also assumed the arms of Portman which he quartered with his paternal arms of Berkeley of Stoke Gifford, placing the Portman arms in the 1st and 4th quarters of greatest honour. His grandson Henry William Portman gave his name to Portman Square in London (begun in 1764), and was grandfather of Edward Berkeley Portman, 1st Viscount Portman (1799-1888). Bryanston Square is named after Bryanston, the seat and estate purchased by Sir William in Dorset shortly before his death. Sources History of Parliament, House of Commons, Members 1660-1690,