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).
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.
Johan de Witt was Grand Pensionary of Holland, an office with powers similar to that of a Prime Minister cum Foreign Secretary combined. He led the country during the first stadtholder-less time from 1650 to 1672 when Republicans saw their chance to get more power for themselves personally at the expense of the House of Orange.