In the month of August, 1791, the Duke of Chartres left Vendome with his regiment, and went to Valenciennes, where he spent the winter. He had been appointed commandant of that place, and, young as he was, discharged the important duties of the position with ability and firmness, which secured for him a very high reputation. The emigrant nobles had assembled on the French frontier, in the electorate of Treves, where they were organizing their forces for the invasion of France. It was understood that Leopold II., then Emperor of Germany, was co-operating with them, and was forwarding large bodies of troops to many points along the German banks of the Rhine for a crusade into France. The French government demanded of the emperor an explanation of his intentions. He replied: "We do not know of any armaments in the Austrian states which can be magnified into preparations for war." Though Louis XVI. was in cordial sympathy with the emigrants, and, by his secret agents, was urging the Emperor of Austria to lend him troops to aid in crushing the revolution in France, still he was compelled not only to dissemble, but on the 20th of April, 1792, publicly to declare war against the Emperor of Austria, who was brother of his queen, Maria Antoinette. The Duke of Orleans, _Egalite_, begged permission of the king to join the armies of revolutionized France in their march against Austria, and to take with him his two oldest sons, the Duke of Chartres (Louis Philippe), and the Duke of Montpensier. In the campaign of 1792, which ensued, both of these young men acquired distinction and promotion. General Biron, in command, wrote to the minister of war: "Messieurs Chartres and Montpensier have accompanied me as volunteers, and, being exposed for the first time to a brisk fire from the enemy, behaved with the utmost heroism and intrepidity." The Duke of Chartres, in command of a brigade of dragoons, was soon after transferred to a corps at Metz, under General Kellerman, who subsequently obtained such renown in the wars of the Empire. When the Duke of Chartres first appeared at head-quarters, General Kellerman, not knowing who he was, and surprised by his youthful appearance, exclaimed: "Ah, monsieur! I never before have had the pleasure of seeing so young a general officer. How have you contrived to be made a general so soon?" The duke replied: "By being a son of him who made a colonel of you." They clasped hands cordially, and a warm friendship commenced between them.