I’m afraid you’ve got dragons by Peter S. Beagle
If you recall, he’s the same author who wrote “The Last Unicorn”, often remembered as a very kitch movie version.
“I’m afraid you’ve got dragons” is also available in German under the title of “Ich fürchte, ihr habt Drachen”.
In the kingdom of Bellemontagne dragons are common and come up in all kinds of sizes, the small vermin-like creatures, up to the fabled Kings, which have not been seen for ages. Gaius Aurelius Constantine Heliogabalus Thrax, who would rather liked to be called Robert, has inherited the craft of dragon exterminator from his father. He doesn’t like his job, though. He would rather be a valet of some prince or king. Yet, he keeps some dragons at home as pets.
He gets hired by the king of Bellemontagne to exterminate all the dragons on the castle, as his daughter, Princess Cerise is expecting Crown Prince Reginald from Corvinia, a neighbouring country.
You probably would expect some story of Cerise and Reginald meeting some obstacles until they finally get married at the end, but despite the book being a fairytale, it’s much much different.
To cut it short: All three of them, Cerise, Reginald and Robert discover what they are made of. I’m not saying more, because the way to the end of the story is the fascinating bit.
I’m recommending the book highly, either in English or German, which I’m considering buying me a copy of too, because it’s that good.