An older brother, Lieutenant Robert Septimus Grenfell, 21st (Empress of India's) Lancers, was killed in a cavalry charge during the Battle of Omdurman in 1898.

[1] An Etonian who represented his school at cricket, Grenfell joined the army in 1900 and first served in the Second Boer War in the King's Royal Rifle Corps.

Grenfell was 33 years old, and a captain in the 9th (Queen's Royal) Lancers, British Army during the First World War when the following deed during the action of Elouges took place for which he was awarded the VC.

On 24 August 1914 at Audregnies, Belgium, Captain Grenfell rode with the regiment in a charge against a large body of unbroken German infantry.

The citation was gazetted on 16 September 1914 and read: For gallantry in action against unbroken infantry at Andregnies, Belgium, on 24th August 1914, and for gallant conduct in assisting to save the guns of the 119th Battery, Royal Field Artillery, near Doubon the same day.