The Royal Family had always lived with a magical beast known formerly for his vile stench, and more currently for his attraction to other vile stenches. They kept him around for... actually, it's not very well understood why they kept him around.
He had been part of the Queen's life from the time the King had first started courting her, and simply remained something to be put up with. A Castle wasn't a home without a magical beast of one kind or another, some might say. As the beast's bad behaviours like shedding its fur, sharpening its claws, stealing food, sitting where he wasn't wanted and even leaving smelly 'gifts' around the castle whittled away their patience, the King and Queen (though especially the King) became increasingly vexed with him.
They did, however, discover one particular notable gift the beast had - he was wonderful with small children. While he had been terrorized and chased by visiting children in the past, he always tolerated whatever the two princes could dish out, and at worst, he would simply run and hide when he'd had enough. Dragons and Ogres could pose quite a threat to children that misbehaved, but the Stench Beast always put up with various transgressions; transgressions that will not be described here, but are on a par with what you'd imagine a Shark Boy and a Lightning Kid could do at their worst.
With the Lightning Kid's increasing mobility, the Stench Beast seemed almost inured to the fear of the boys. He was almost coy in his retreats, seeming to say: "Oh, I've escaped from you to the safety of... a spot merely three feet away from where you last threatened me."
It was the King's suspicion that the love the Stench Beast bore for the Queen had come to extend to her offspring, and his tolerance of their semi-violent ministrations was his way of expressing it.
It was the Stench Beast's opinion, that the King was mostly alright, as humans tended to go...