After his mother's death in 1898, his father remarried to the English born actress, Eleanor Robson.
In 1916, Belmont attended the Citizens' Military Training Camp in Plattsburgh, New York, before shipping off to France in May 1918 as a lieutenant in the Headquarters Troop of the 78th Division.
[2] Belmont was a champion polo player, with a six-goal handicap, in 1923, and was a member of the team (along with Devereux Milburn, Thomas Hitchcock Jr., and Robert Early Strawbridge Jr.) that won the National Open Championship from the British Army four.
[5] They divorced in 1916 and his second marriage took place on September 20, 1916, he was married to Carolyn Brown Hulbert (1892–1970) in Middleburg, Virginia.
After an illness of several days, Belmont died of pneumonia at his home, known as Belray in Middleburg, near Leesburg, Virginia, on April 5, 1934.