His father, John Henry Siddons, represented a British bank in Alexandria; he died of hyperthermia a year after his son was born.

When Mowbray was five, his mother died, burnt alive in a domestic accident caused by lamp fuel.

Left an orphan, the boy was adopted by his aunt, his mother's sister, and her husband, George Mowbray.

[3] After a year at the United States Military Academy at West Point,[4] he went to Paris and entered the atelier of Leon Bonnat in 1879, his first picture, Aladdin, bringing him to public notice.

[8] Among Mowbray's pupils were the painters Mortimer Lichtenauer, Florence Wolf Gotthold[9] and Clara Taggart MacChesney.