sentences:  Duncan is the only son of the five children of Frank L. Duncan, a district conservationist for the U.S. Department of Agriculture in Vernon, and the former Robena Formby, who married Joe King of San Marcos and later Roaring Springs after the death of Frank Duncan.Robena Duncan King was the sister of Marshall Formby, an attorney and radio station owner from Plainview in Hale County, who served as county judge of Dickens County, as a state senator from Lubbock (then District 30) from 1941 to 1945, and was thereafter an influential member of the Texas Highway Commission.Marshall Formby was also an unsuccessful Democratic gubernatorial candidate in 1962, having lost out to John B. Connally, Jr. Duncan was a cousin of the late radio broadcaster Clint Formby of Hereford, Texas.