He was appointed to the post by His Catholic Majesty King Carlos III and he forged a new alliance between the kingdoms of Spain and France in cooperation with the French Secretary of State Étienne François, duc de Choiseul. This was the "Third Family Compact" so named because of the Bourbon Royal Family that reigned over both France and Spain. He was in close contact also with the American Arthur Lee in Madrid, the envoy of the rebel American government for Spain and Prussia. Lee later helped draw up the alliance with France but is seldom noted because of a falling out with the more famous and popular Benjamin Franklin. Of course, he was insistent that Spain recognize the United States and join in the war against Britain immediately but the Duke of Grimaldi held back and delayed until Spain was in a stronger position, writing to Lee, "You have considered your own situation, and not ours. The moment is not yet come for us. The war with Portugal — France being unprepared, and our treasure ships from South America not being arrived — makes it improper for us to declare immediately." He was referring, of course, to the long-standing alliance between Portugal and Great Britain. However, the Duke of Grimaldi reassured Lee of Spanish sympathy and informed him of the large stores of clothing and gunpowder delivered to New Orleans and Havana that were to be smuggled in to help the American patriots with more on the way.
Eventually, of course, the Kingdom of Spain did recognize the United States and join in declaring war on Great Britain with the Treaty of Aranjuez in 1779. Spanish troops actually played an important part both by their numerous victories over the British on the gulf coast and by diverting British focus and forces with the siege of Gibraltar. In the end, Spain was able to win back almost everything that they had lost previously to Britain in the Seven Years' War, though not Gibraltar which, of course, remains under the British Crown to this day. So, there was a member of the Grimaldi family that played an often overlooked but critical part in the winning of American independence and the birth of the United States. It was during the war, in 1777, that His Catholic Majesty King Carlos III granted him the title first Duke of Grimaldi. He was awarded the Order of the Golden Fleece for his service, made a Grandee of Spain and died in 1789.
