[1] He was commissioned into the Grenadier Guards and fought in the First World War and became a Lieutenant and received the Military Cross.

[1] He was promoted to Private Secretary upon the accession of Edward VIII that same year, contributing to some delicate negotiations between the new king and the British government in the run up to the king's abdication in December 1936; he continued in this role under George VI until his early retirement in 1943.

This was particularly reflected in Hardinge's warning letter to Edward, received on 13 November 1936, which showed evidence of prior consultation with Prime Minister Stanley Baldwin, who, with his cabinet, had serious misgivings about the suitability of Mrs Wallis Simpson as the possible spouse of the monarch.

[4] The precise nature and extent of his loyalty were thus constitutional—doing what he thought was right in his post as Private Secretary to the Sovereign.

His wife Helen wrote his biography Loyal to Three Kings, William Kimber, London 1967.