Who was the last french king and when did he die?

Officially, Louis XVI and Marie Antoinette. They were the last real King and Queen of France.

After the Napoleonic period (who turned France into an empire), the French monarchy was restored for some time, but only as a constitutional monarchy, meaning there were a King and Queen of France, but only in name. It was purely a title and they had no real reigning power. The last king and queen of that constitutional monarchy were Louis Philippe I and Maria Amalia (Marie Antoinette's niece).