 He was the only son of Myles Gerald Keon, barrister, and on his mother's side was descended from the Fallons of Runnymede, County Roscommon.Both parents dying in his infancy, Keon was left to the care of his maternal grandmother, and later to that of his uncle, Francis Philip, Count Magawly.He studied at the Jesuit college at Stonyhurst, where he wrote the prize poem on Queen Victoria's accession (Stonyhurst Magazine, no.