In a European context it’s purely fantasy. Take a look at this National Geographic map showing crocodilian ranges. Historically the ranges were larger; for example there were crocodiles in the lower Nile until the 20th century, and we have ancient mentions of crocodiles in North Africa as well as the Levant. But there haven’t been any type of crocodilians (alligators, caimans, crocodiles, or gharials) living within in Europe within the time frame of modern humans. That said there’s no reason an enterprising noble couldn’t import one. Much of Southern Europe is warm enough to support a variety of species. But there’s no reason to suspect that anyone ever did.