Aesop's Viper …
There are many variations on the Aesop fable “The Farmer and the Viper” but, basically it is the story of the kindly old farmer who feels sorry for a snake who appears to be freezing to death. He picks it up and cuddles it under his warm jacket only to be repaid by a lethal snake bite as soon as the reptile recovers. As the farmer lays dying the last words he hears are these: “Don't blame me,” says the snake, "You knew what I was when you picked me up."
Of course I had to look up the definition of fabulist and this is what it says in the Oxford Dictionary.
1. A liar, especially one who invents elaborately dishonest stories. 'a born fabulist with an imagination unfettered by the laws of logic and probability'.
Need I say more?