Charles III was Prince of Monaco and Duke of Valentinois from 20 June 1856 to his death. He was the founder of the famous casino in Monte Carlo, as his title in Monegasque and Italian was Carlo III. He was born in Paris Charles Honoré Grimaldi, the only son of Florestan I of Monaco and Maria Caroline Gibert de Lametz.
He succeeded his father Prince Florestan I in 1856. During his reign, the towns of Menton and Roquebrune, constituting some 80 percent of Monegasque territory, were formally ceded to France, paving the way for formal French recognition of Monaco's independence. Rebellions in these towns, aided by the Kingdom of Sardinia, had exhausted Monaco's military resources for decades.
Prince Charles III died at Château de Marchais on 10 September 1889. He was succeeded by his son Albert I of Monaco.