Felix Salm - Salm Prince Felix Salm - Salm ( 1828 – 1870 ) was a Prussia n military officer of noble birth and a soldier of fortune . Salm - Salm served in the Schleswig - Holstein Army ( Prussian Army ) , Austrian Army , the Union Army during the American Civil War , the army of Emperor Maximilian I in Mexico and thereafter in the Prussian Army . He was killed in action during the Franco - Prussian War . Life . Felix Constantin Alexander Johan Nepomuk , prince Salm Salm , was born in Anholt , Prussia , 25 December 1828 . Felix was the son of the reigning Prince zu Salm Salm . He grew up training to be a soldier at a cadet - school in Berlin , Germany and became an officer in the Prussian cavalry in 1846 . Early on he participated in the First Schleswig War between Northern Germany and Denmark , where he demonstrated bravery in battle . After the war he joined the Austrian army , serving in the Austro - Sardinian War of 1859 . In 1861 , he came to the United States and offered his services to the Union Army in the American Civil War . He was given a colonel ' s commission and assigned to the staff of Brigadier General Louis Blenker . It was at this time that he began to court a red - haired American woman of Indian descent named Agnes Leclerc Joy . Felix would marry her in August 1862 . Agnes Salm - Salm would end up joining Felix on the battlefield because she could not bear being without him . That winter he took command of the 8th New York Volunteer Infantry Regiment but would only remain there through the winter . He was appointed colonel of the 68th New York Volunteer Infantry Regiment in June , 1864 , serving under Brigadier General James B . Steedman in Tennessee and Georgia , and toward the end of the war was assigned to the command of the post at Atlanta . Salm - Salm was mustered out of the volunteers on November 30 , 1865 . On January 13 , 1866 , President Andrew Johnson nominated Salm - Salm for appointment to the grade of brevet brigadier general , to rank from April 13 , 1865 and the U . S . Senate confirmed the appointment on March 12 , 1866 . After the American Civil War was over , Salm - Salm offered his services to Emperor Maximilian I of Mexico and embarked for Mexico in February , 1866 . Maximilian was actively promoting American soldiers to migrate to Mexico after the war to improve relations with the country . Salm - Salm was an interesting case because he had fought for the Union while most of the Americans who moved to Mexico after the Civil War had fought for the Confederacy . By the summer he was appointed colonel and became the emperor ' s aide - de - camp and chief of his household . He was captured at Querétaro along with the emperor but not before he made a brave charge with his hussar cavalry in an attempt to save Maximilian from the surrounding Mexican Republican army under Benito Juárez . Soon after Maximilian ' s execution , he returned to Europe , re - entered the Prussian army as major in the grenadier guards , and was killed at Saint - Privat - la - Montagne during the Battle of Gravelotte in the Franco - Prussian War . Prince Felix Salm - Salm is buried in Anholt , Westphalia , Germany . His memoirs were edited by German author Otto von Corvin .