The king chases the cat. H. Ford.

Cats play a prominent role in a wide variety of fairy tales, but the one I first think of is Puss in Boots. In any case, I imagine I'd be rather put out too if someone stepped on my tail and changed me unwillingly back into human form, foiling my enchantment. I'm not sure I'd curse the king's unborn son, but I'd definitely be cursing someone. 

“You shall marry the Princess because you have been able to break the enchantment, but I will have my revenge. You shall have a son, who will never be happy until he finds out that his nose is too long, and if you ever tell anyone what I have just said to you, you shall vanish away instantly, and no one shall ever see you or hear of you again.”