Looking for a good pub quiz question? This one might catch some people out. Europe has a surprising number of monarchies, ranging from the well known to the obscure. They cover the spectrum from constitutional monarch through power sharing to absolute ruler. The youngest monarchy was instituted in 1929 (and that's a clue).
Princess Antoinette of Monaco was born as the first child of Princess Charlotte of Monaco and was the older sister of Prince Rainier III of Monaco. In her time, she was good for quite a few scandals. Highly eccentric, she was also well beloved by the citizens of Monaco. She took two turns at being First Lady of the Principality of Monaco and was president of its animal welfare charity SPA.
During World War II, the Principality Monaco was a neutral state. It was fiercely contested by Germany and Italy who had mutually opposing and exclusive ideas as to its future. Prince Louis II had been brought up in Germany and was a general in the French army. He played his connections for all they were worth in trying to keep the country afloat.
There are Princes and Princesses, and then there are Princes and Princesses. Some are Royal or more, some are not. The problem lies in geography. Depending on where the title came from, the title of Prince does not mean the same thing. The puzzle can be solved given some knowledge of geography and history, and quite some of the muddle derived from translating foreign titles into English.