The drawing is illustrated in the book, 'Warrior, The Amazing Story of a Real War Horse' by General Jack Seely. A great friend of Sir Winston Churchill, General Seely went to war with Warrior in 1914 and led many battles, including the vital charge at Moreuil Wood on 30th March 1918. They returned home to the Isle of Wight with Warrior after the war and the horse became a legend. He won the Isle of Wight Point to Point on 30th March 1918, exactly four years after the charge at Moreuil Wood.
Warrior died in 1941 aged 33 and his obituary, which was printed in the Evening Standard, read 'The Horse the Germans Could Not Kill'.
The portrait has come to auction at Cheffins from a private Suffolk collection and is estimated at £3,000 - £5,000.
The catalogue will be available two weeks prior to the sale.