blackguard
The heroine may call the hero a blackguard at first, but in the end only the villain fits the description.
Merriam-Webster
A rude or unscrupulous person : a person who uses foul or abusive language
Wiktionary
A vulgar and uncouth person. One who has a less than trustworthy level of inhibition.
1811 Vulgar Tongue
Black guard — A shabby, mean fellow; a term said to be derived from a number of dirty, tattered roguish boys, who attended at the Horse Guards, and Parade in St. James’s Park, to black the boots and shoes of the soldiers, or to do any other dirty offices. These, from their constant attendance about the time of guard mounting, were nick-named the black-guards.
