Thelma, Viscountess Furness (August 23, 1904 – January 29, 1970), born Thelma Morgan, was a mistress of King Edward VIII, who later became the Duke of Windsor, she preceded Wallis Simpson in his affections. Her first name was pronounced in Spanish fashion as "TEL-ma." Her niece is fashion designer Gloria Vanderbilt.
Born in Lucerne, Switzerland, she was a daughter of Harry Hays Morgan Sr, an American diplomat who was U.S. consul in Buenos Aires and in Brussels, and his half-Chilean, half-Irish-American wife, Laura Delphine Kilpatrick. Married in 1893, they were divorced in 1927.
Her maternal grandfather was a Union general, Hugh Judson Kilpatrick (1836–1881), who was also U.S. minister to Chile, and through her maternal grandmother Luisa Fernandez de Valdivieso, who was a niece of Crescente Errázuriz Valdivieso, Archbishop of Santiago, she reportedly was a descendant of Spain's royal house of Navarre.
Thelma Morgan had two sisters: Gloria (her identical twin, the mother of Gloria Vanderbilt, the fashion designer and artist and mother of news anchor Anderson Cooper) and Laura Consuelo Morgan (aka Tamar), who was married to Count Jean de Maupas du Juglart, a French nobleman;